Despite many of us continue to see Bitcoin Layer One as the only way forward, and Lightning as the unique supporting L2, The ecosystem surrounding Bitcoin is growing exponentially. This website helped me have a broader and detached view. Here the repo for contributions https://github.com/layerztec/layers2

The Emergent Architecture of Bitcoin's Second Layer

A Cartography of Possibilities

There exists today a living catalog of human ingenuity, quietly accumulating at layers2.com, that maps 83 distinct approaches to a singular problem: how to extend Bitcoin beyond its foundational constraints without compromising the philosophical commitments that made it revolutionary in the first place.¹ This is not merely a technical challenge. It represents something more profound—a collective intelligence experiment in distributed consensus about what money can become when freed from the gravitational pull of both state control and blockchain bloat.

The aggregate investment in these Layer 2 architectures has reached $1.8 billion, a figure that captures not just capital allocation but a bet on inevitable trajectories. From 2021 through 2025, this investment has accelerated, suggesting we're witnessing not the peak of innovation but rather its adolescence. The projects catalogued here represent competing visions of the future, each one a small answer to a large question about scalability, sovereignty, and the nature of digital scarcity.²

The Native Foundations: Where Bitcoin Remembers Itself

The seven projects classified as Bitcoin Native carry within them an orthodoxy, a determination to scale Bitcoin without fundamentally altering its DNA. The Lightning Network,³ launched in 2015, remains the elder statesman of this category—a state channel architecture that moves transactions off-chain while anchoring security to Bitcoin's base layer. It doesn't try to be something Bitcoin isn't; it amplifies what Bitcoin already is.

Spark,⁴ positioned as the featured project and launched in 2022, employs statechain technology to enable transfer of Bitcoin ownership without on-chain transactions for every exchange. This represents a subtle philosophical shift: instead of broadcasting every transaction to the world, ownership changes hands through cryptographic attestation, with the blockchain serving as final arbiter only when disputes emerge or users exit the system. Mercury Layer⁵ pursues a similar path, demonstrating that multiple teams have independently converged on statechains as a viable scaling primitive.

Then there's RGB,⁶ operational since 2016, which takes client-side validation to its logical extreme. Transactions occur between parties who validate state transitions locally, with Bitcoin's blockchain used merely as a commitment layer. This inversion—where the blockchain doesn't process transactions but simply bears witness to their having occurred—challenges our assumptions about what a blockchain must do to remain useful. Ark⁷ extends this thinking further with Virtual UTXOs, creating a structure where Bitcoin's native UTXO model becomes abstracted and multiplied across second-layer constructions.

The diversity here belies the small number of projects. Lnfi Network⁸ and Lygos Finance⁹ add application-specific layers—the former an appchain, the latter focused on Discreet Log Contracts for complex financial instruments. What unites them is loyalty to Bitcoin's base layer combined with creative interpretation of how that loyalty can manifest.

The Rollup Renaissance: Thirty Experiments in Compressed Validity

The rollup category contains 30 projects, making it the most populated landscape in the Bitcoin Layer 2 ecosystem. This proliferation tells us something important: the rollup paradigm, proven on Ethereum, has been recognized as sufficiently powerful and flexible to warrant extensive adaptation to Bitcoin's different consensus model and scripting limitations.¹⁰

Zk-rollups dominate the rollup category, with projects like Hemi,¹¹ Citrea,¹² B² Network,¹³ Merlin Chain,¹⁴ and GOAT Network¹⁵ all pursuing zero-knowledge proof systems to compress transaction validity into cryptographic attestations. The elegance of zk-rollups lies in their mathematical certainty—they don't ask the base layer to trust that transactions were executed correctly; they prove it with succinct cryptographic evidence. This transforms Bitcoin from a transaction processor into a verification layer, allowing thousands of transactions to be validated through a single proof.

The emergence of projects like Alpen Labs,¹⁶ ZKM,¹⁷ Bison,¹⁸ Hacash,¹⁹ Lightec,²⁰ and LumiBit²¹—many still in testnet—suggests we're in an experimental phase where teams are exploring different trade-offs in proof systems, data availability assumptions, and bridge architectures. TunaChain,²² SatoshiSync,²³ and SatoshiVM²⁴ each represent distinct approaches to the same fundamental challenge: how to inherit Bitcoin's security while achieving transaction throughput that makes decentralized applications viable.

Optimistic rollups offer an alternative philosophy. BOB,²⁵ BitLayer,²⁶ Biop,²⁷ and Rollux²⁸ implement fraud-proof systems where transactions are assumed valid unless challenged, creating a different security model that trades immediate finality for greater efficiency. The optimistic approach reflects a different trust assumption—not that humans are trustworthy, but that economic incentives to catch fraud can be structured reliably enough to approximate trustlessness.

What's particularly fascinating is the presence of Starknet²⁹ and ZeroSync,³⁰ which bring established Layer 2 technologies from other ecosystems into Bitcoin's orbit. Starknet, launched in 2022 as a bridge, and ZeroSync's ongoing development of zero-knowledge proof systems for Bitcoin state validation, represent knowledge transfer between blockchain ecosystems—a technological pollination that accelerates innovation across the entire space.

The zkEVM experiments, like zkBase,³¹ push even further by attempting to bring Ethereum Virtual Machine compatibility to Bitcoin through zero-knowledge proofs. This isn't about making Bitcoin into Ethereum; it's about making Bitcoin interoperable with the tooling, languages, and developer ecosystems that have flourished elsewhere. It's a recognition that technology stacks are not tribal affiliations but instruments to be deployed where they serve human needs.

Additional notable rollup projects include Psy Protocol,³² Fiamma,³³ Zulu Network,³⁴ Elastos,³⁵ Rooch Network,³⁶ and several others, each exploring unique approaches to Bitcoin scaling through rollup architectures.

Sidechains: The Parallel Realities

With 34 projects, sidechains represent the most heterogeneous category, a collection of approaches unified only by their strategy of creating parallel chains that interact with Bitcoin through bridges and peg mechanisms. This diversity is not accidental—it reflects fundamental disagreements about the optimal trade-offs between security, sovereignty, and functionality.

Liquid Network,³⁷ operational since 2018, and Rootstock,³⁸ running since 2015, represent the established guard. Liquid employs a federation model where a consortium of entities manages the two-way peg between Bitcoin and the sidechain, trading some decentralization for functionality like confidential transactions and asset issuance. Rootstock takes a different approach, implementing a Bitcoin-merge-mined sidechain with smart contract capabilities, allowing developers to build Ethereum-style applications while remaining anchored to Bitcoin's proof-of-work security.

Stacks,³⁹ launched in 2019 with its STX token, pioneered the "anchored chain" approach where blocks on the sidechain are tied to Bitcoin blocks through a unique consensus mechanism called Proof of Transfer. This creates a symbiotic relationship where Stacks miners compete for block production rights by sending Bitcoin to existing Bitcoin holders, creating a novel economic link between the two chains.

The newer entrants reveal how the design space continues to expand. Botanix⁴⁰ experiments with a "Spiderchain" architecture in testnet, presumably exploring novel consensus or security models. Bitfinity⁴¹ and BEVM,⁴² both on mainnet, implement zk-rollup technology within a sidechain framework, creating hybrid architectures that combine the sovereignty of independent chains with the cryptographic compression of rollups.

The federation-based approaches—Liquid Network, BVM,⁴³ and Bitway⁴⁴—acknowledge a pragmatic reality: sometimes the most efficient path to functionality requires accepting trust assumptions different from Bitcoin's base layer, but structuring those assumptions through explicit multi-signature federations rather than single points of failure. This isn't a compromise of principles but rather a graduated security model where users can choose their preferred point on the spectrum between trustlessness and functionality.

Projects like Core DAO,⁴⁵ ExSat,⁴⁶ Side Protocol,⁴⁷ bitSmiley,⁴⁸ and the broader collection of sidechains with mainnet deployments demonstrate that demand exists for Bitcoin-adjacent chains that optimize for different properties than Bitcoin itself. Some prioritize transaction speed, others smart contract expressiveness, still others novel consensus mechanisms. The sidechain model permits this Cambrian explosion of experimentation precisely because sidechains don't constrain Bitcoin's base layer—they extend outward from it.

What's particularly notable is the geographic and philosophical diversity represented here. Projects like Conflux,⁴⁹ Map Protocol,⁵⁰ Nervos,⁵¹ and ICP⁵² bring perspectives from different development communities, each carrying assumptions and priorities shaped by distinct technological traditions. MVC,⁵³ Kadena,⁵⁴ Libre,⁵⁵ Mintlayer,⁵⁶ Rosetta Network,⁵⁷ Plasma,⁵⁸ BounceBit,⁵⁹ Anduro,⁶⁰ Midl,⁶¹ Ailayer,⁶² and Sovryn⁶³—these names represent teams that looked at Bitcoin and saw different missing pieces, then built different solutions accordingly.

Meta Protocols: Bitcoin as Substrate

The five projects categorized as Meta Protocols represent perhaps the most philosophically interesting development in Bitcoin's evolution. These aren't Layer 2s in the traditional sense—they're protocols built directly on Bitcoin's base layer that reinterpret what Bitcoin's blockchain can mean.⁶⁴

Ordinals,⁶⁵ launched in 2023, created a system for inscribing arbitrary data into individual satoshis, effectively creating NFTs on Bitcoin by treating each smallest unit of Bitcoin as a unique, numbered entity. This wasn't a technical innovation in the conventional sense—the capability always existed—but rather a social and interpretive innovation that recognized that Bitcoin's ledger could serve as a permanent, censorship-resistant data store.

BRC-20,⁶⁶ also from 2023, extended this logic to create a token standard using ordinal inscriptions, enabling fungible tokens to exist as data within Bitcoin transactions. Runes,⁶⁷ launched in 2024, offers an alternative fungible token protocol with different technical trade-offs. BTKN⁶⁸ adds yet another token standard, while Alkanes,⁶⁹ the newest entry from 2025, brings smart contract capabilities through the meta protocol approach.

What unites these projects is a radical conservatism: they accept Bitcoin exactly as it is and find new meanings within existing affordances. They don't fork Bitcoin, don't create sidechains, don't implement new cryptographic primitives. They simply look at Bitcoin's data structure and ask, "What else could this mean?" The answer, it turns out, is quite a lot.

This represents a profound shift in how we think about blockchain functionality. Rather than adding features through protocol changes or separate layers, meta protocols demonstrate that rich functionality can emerge from creative interpretation of existing structures. They're proof that Bitcoin's apparent simplicity contains multitudes—that what looks like a constraint from one angle becomes a canvas from another.

The Experimental Frontier: Other Architectures

The seven projects categorized as "Other" resist easy classification, which is precisely what makes them interesting. These are the outliers, the approaches that don't fit comfortable taxonomies, the experiments that might fail or might reveal entirely new possibility spaces.

Babylon,⁷⁰ operational on mainnet since 2022 with its BABY token, has reimagined Bitcoin staking—a concept that seems contradictory given Bitcoin's proof-of-work consensus. Yet Babylon found a way to enable Bitcoin to secure other chains through cryptographic commitments and time-locked transactions, creating a staking protocol that extends Bitcoin's security guarantees outward to other ecosystems.

Fedimint⁷¹ and Cashu⁷² represent the Chaumian Ecash revival, bringing David Chaum's 1980s innovations in digital cash to Bitcoin's modern context.⁷³ Fedimint, in testnet since 2022, implements a federated mint system where trusted parties can issue ecash tokens backed by Bitcoin, trading full decentralization for privacy and scalability in contexts where trust relationships already exist—like community banks or family treasuries. Cashu, on mainnet since 2022, offers a similar architecture with different implementation choices. Bitcredit Protocol⁷⁴ extends this concept further with its eIOU token system.

The data availability projects—Riema Labs,⁷⁵ Bool Network,⁷⁶ Gelios,⁷⁷ Nubit,⁷⁸ and Syscoin⁷⁹—address a different bottleneck entirely. These protocols focus on ensuring that data necessary to verify blockchain state remains accessible, a seemingly mundane concern that becomes critical as blockchains scale. Bool Network has been operational since 2018, making it one of the older projects in the entire catalog, while newer entrants experiment with different approaches to the same fundamental challenge.

Drivechain,⁸⁰ in testnet since 2023, implements a controversial proposal for Bitcoin sidechains secured through miner validation, allowing Bitcoin miners to secure independent chains through a mechanism that's provoked significant debate within the Bitcoin community. Its inclusion here acknowledges that controversial approaches deserve experimentation even when consensus remains elusive.

The presence of projects like Nostr Assets Protocol,⁸¹ OmniBOLT,⁸² both implementing state channels, and RGB++,⁸³ with its client-side validation, demonstrates that even within established categories, new approaches continue to emerge. Sova⁸⁴ experiments with precompiles, THORChain⁸⁵ operates a liquidity pool protocol, and Mezo,⁸⁶ Arch,⁸⁷ and Satoshi Protocol⁸⁸ add additional dimensions to the experimental frontier.

The Pattern Beneath the Chaos

What emerges from this catalog of 83 projects is not chaos but rather a distributed search algorithm—thousands of engineers, cryptographers, and entrepreneurs independently exploring the vast solution space of blockchain scaling.⁸⁹ The $1.8 billion in investment represents not just capital but attention, the scarcest resource in our information economy.

The timeline is revealing. Rootstock and Lightning Network from 2015, Syscoin from 2014, RGB from 2016—these pioneers established that Bitcoin could scale beyond its base layer. The 2022-2024 period shows explosive growth in the rollup category, reflecting the migration of proven paradigms from Ethereum to Bitcoin's different context. The 2025 projects, still emerging, suggest the exploration continues to accelerate rather than consolidate.

What's particularly striking is the distribution across mainnet and testnet. Roughly half these projects have launched on mainnet, accepting real economic risk and serving real users. The other half remain in testnet, still discovering what works. This balance suggests a healthy ecosystem—neither paralyzed by caution nor reckless with premature deployment.

The native token distribution tells another story. While Bitcoin Native projects predominantly stick with BTC, the rollup and sidechain categories almost universally introduce new tokens. This isn't merely about fundraising or speculation; tokens serve as coordination mechanisms, aligning incentives between developers, validators, and users in systems that can't rely solely on Bitcoin's existing economic structure.

The open-source nature of this catalog, maintained by Layerz Wallet, reflects the collaborative ethos that built Bitcoin in the first place. This isn't a commercial directory or marketing platform but rather a commons, a shared resource for understanding the evolving topology of Bitcoin's second layer.

The Inevitable Trajectory

We are watching the decentralization of decentralization—not just value exchange but the very architecture of value exchange becoming heterogeneous, specialized, adapted to different use cases and trust assumptions. Bitcoin's base layer remains, deliberately constrained, optimized for security and immutability. But around it grows an ecosystem of interpretations, extensions, and alternatives, each one a hypothesis about what people need from their monetary infrastructure.⁹⁰

Some of these 83 projects will fail. Many, probably. But their failures will teach as much as their successes, and the successful approaches will likely combine insights from multiple attempts. This is technology evolving not through central planning but through selection pressures applied by users voting with actual economic value.

The future being built here isn't Bitcoin replacing fiat currency or one dominant Layer 2 winning market share. It's something stranger and more interesting: a Cambrian explosion of monetary technologies, each optimized for different contexts, collectively creating an ecosystem where users can navigate between security, speed, privacy, and programmability according to their needs.

This catalog at layers2.com is not a complete map—it's a snapshot of an ongoing exploration. By the time you read this, new projects will have launched, others will have pivoted or shut down, and the taxonomy itself will have evolved. That's precisely as it should be. The technology is not stabilizing; it's accelerating. And somewhere in these 83 experiments lies the infrastructure for human coordination we haven't yet imagined but will someday take for granted, the way we now take email for granted, or mobile phones, or Bitcoin itself.

The second layer isn't being built on top of Bitcoin. It's being built around it, beside it, through it, interpreting it—an emergent architecture that respects the foundation while refusing to be constrained by it. That's not a contradiction. It's the only way anything genuinely new ever emerges.

Footnotes

layers2.com - An open-source directory tracking Bitcoin Layer 2 projects, maintained by Layerz Wallet. ↩
For context on Bitcoin scaling debates, see: Antonopoulos, A. M. (2017). Mastering Bitcoin: Programming the Open Blockchain. O'Reilly Media. ↩
Lightning Network - https://lightning.network - Poon, J., & Dryja, T. (2016). "The Bitcoin Lightning Network: Scalable Off-Chain Instant Payments." ↩
Spark - https://www.spark.info - Statechain implementation for Bitcoin scaling. ↩
Mercury Layer - https://mercurylayer.com - Statechain protocol enabling off-chain Bitcoin transfers. ↩
RGB - https://rgb.info - Client-side validation protocol for Bitcoin. See also: Orlovsky, M. (2019). "RGB Protocol Specification." ↩
Ark - https://ark.tech - Virtual UTXO protocol by Burak Keceli. ↩
Lnfi Network - https://lnfi.network - Lightning Network-based appchain. ↩
Lygos Finance - https://lygos.finance - DLC-based financial protocol. ↩
For rollup fundamentals, see: Buterin, V. (2021). "An Incomplete Guide to Rollups." Ethereum Research. ↩
Hemi - https://hemi.xyz - Bitcoin zk-rollup project. ↩
Citrea - https://citrea.xyz - Zero-knowledge rollup for Bitcoin. ↩
B² Network - https://www.bsquared.network - Bitcoin Layer 2 using zk-rollup technology. ↩
Merlin Chain - https://merlinchain.io - Bitcoin Layer 2 network with native BTC assets. ↩
GOAT Network - https://goat.network - Zk-rollup focused on Bitcoin DeFi. ↩
Alpen Labs - https://alpenlabs.io - Zero-knowledge proof research for Bitcoin. ↩
ZKM - https://zkm.io - Zero-knowledge virtual machine for Bitcoin. ↩
Bison - https://bisonlabs.io - Bitcoin zk-rollup in development. ↩
Hacash - https://hacash.org - Multi-layered cryptocurrency system. ↩
Lightec - https://lightec.io - Zk-rollup project for Bitcoin. ↩
LumiBit - https://lumibit.io - Bitcoin Layer 2 using zero-knowledge proofs. ↩
TunaChain - https://tunachain.io - Bitcoin-based zk-rollup network. ↩
SatoshiSync - https://satoshisync.io - Zk-rollup for Bitcoin transactions. ↩
SatoshiVM - https://satoshivm.io - Zero-knowledge virtual machine for Bitcoin. ↩
BOB - https://gobob.xyz - "Build on Bitcoin" optimistic rollup platform. ↩
BitLayer - https://bitlayer.org - First Bitcoin security-equivalent Layer 2 based on BitVM. ↩
Biop - https://biop.io - Optimistic rollup for Bitcoin. ↩
Rollux - https://rollux.com - Syscoin's Bitcoin-merged optimistic rollup. ↩
Starknet - https://www.starknet.io - STARK-based validity rollup, now bridging to Bitcoin. ↩
ZeroSync - https://zerosync.org - Bringing zero-knowledge proofs to Bitcoin with ZKPs for chain state validation. ↩
zkBase - https://zkbase.org - zkEVM implementation for Bitcoin. ↩
Psy Protocol - https://psy.tech - Zk-rollup project. ↩
Fiamma - https://fiamma.io - Bitcoin bridge protocol. ↩
Zulu Network - https://zulunetwork.io - DePIN-focused Bitcoin Layer 2. ↩
Elastos - https://elastos.org - Long-standing blockchain project with Bitcoin sidechain. ↩
Rooch Network - https://rooch.network - Move-based Bitcoin Layer 2. ↩
Liquid Network - https://liquid.net - Federated Bitcoin sidechain by Blockstream for rapid, confidential settlement. ↩
Rootstock - https://rootstock.io - Bitcoin's first smart contract platform, merge-mined with Bitcoin since 2015. ↩
Stacks - https://www.stacks.co - Bitcoin Layer 2 using Proof of Transfer consensus mechanism. ↩
Botanix - https://botanixlabs.xyz - Spiderchain-based Bitcoin Layer 2. ↩
Bitfinity - https://bitfinity.network - EVM-compatible Bitcoin sidechain. ↩
BEVM - https://bevm.io - Decentralized EVM-compatible Bitcoin Layer 2. ↩
BVM - https://bvm.network - Bitcoin Virtual Machine for building Bitcoin Layer 2s. ↩
Bitway - https://bitway.io - Federated Bitcoin sidechain. ↩
Core DAO - https://coredao.org - Bitcoin-aligned Layer 1 using Satoshi Plus consensus. ↩
ExSat - https://exsat.network - Bitcoin data consensus extension network. ↩
Side Protocol - https://side.one - Bitcoin DeFi sidechain. ↩
bitSmiley - https://bitsmileylabs.io - Native stablecoin protocol on Bitcoin. ↩
Conflux - https://confluxnetwork.org - Hybrid PoW/PoS blockchain with Bitcoin connections. ↩
Map Protocol - https://www.mapprotocol.io - Omnichain infrastructure connecting Bitcoin. ↩
Nervos - https://www.nervos.org - Layered blockchain platform designed for interoperability with Bitcoin. ↩
ICP - https://internetcomputer.org - Internet Computer Protocol with ckBTC integration. ↩
MVC - https://mvc.network - MicroVisionChain, a Bitcoin-based blockchain. ↩
Kadena - https://kadena.io - Proof of Work blockchain with Bitcoin parallels. ↩
Libre - https://libre.org - Bitcoin-connected blockchain for financial applications. ↩
Mintlayer - https://mintlayer.org - Bitcoin sidechain for DeFi and tokenization. ↩
Rosetta Network - https://rosetta.network - Bitcoin interoperability protocol. ↩
Plasma - https://plasma.network - Recent Bitcoin sidechain project (2025). ↩
BounceBit - https://bouncebit.io - Bitcoin restaking infrastructure. ↩
Anduro - https://anduro.io - Multi-chain sidechain platform for Bitcoin. ↩
Midl - https://midl.dev - Bitcoin sidechain in development. ↩
Ailayer - https://ailayer.xyz - AI-focused Bitcoin Layer 2. ↩
Sovryn - https://sovryn.com - Bitcoin DeFi platform built on Rootstock. ↩
For meta protocols, see: Rodarmor, C. (2022). "Ordinals Theory Handbook." ↩
Ordinals - https://ordinals.com - Protocol for inscribing data on individual satoshis. ↩
BRC-20 - https://brc-20.io - Token standard using ordinal inscriptions. ↩
Runes - https://runes.com - Fungible token protocol for Bitcoin by Casey Rodarmor. ↩
BTKN - https://btkn.io - Alternative Bitcoin token standard. ↩
Alkanes - https://alkanes.io - Smart contract meta protocol for Bitcoin. ↩
Babylon - https://babylonchain.io - Bitcoin staking protocol extending Bitcoin security to PoS chains. ↩
Fedimint - https://fedimint.org - Federated Chaumian ecash protocol. See: Fedimint Developers (2022). "Fedimint: Federated Chaumian Banks." ↩
Cashu - https://cashu.space - Chaumian ecash system for Bitcoin. ↩
Chaum, D. (1983). "Blind signatures for untraceable payments." Advances in Cryptology. ↩
Bitcredit Protocol - https://bitcredit.network - Chaumian ecash implementation with eIOU. ↩
Riema Labs - https://riemalabs.com - Bitcoin data availability layer. ↩
Bool Network - https://bool.network - Cross-chain data availability protocol (est. 2018). ↩
Gelios - https://gelios.io - Bitcoin data availability solution. ↩
Nubit - https://nubit.org - Data availability layer for Bitcoin. ↩
Syscoin - https://syscoin.org - Long-running Bitcoin-merged blockchain with DA capabilities (est. 2014). ↩
Drivechain - https://drivechain.info - BIP300/301 proposal for Bitcoin sidechains via blind merged mining. ↩
Nostr Assets Protocol - https://nostr-assets.org - Asset protocol built on Nostr and Bitcoin. ↩
OmniBOLT - https://omnibolt.com - Lightning Network extension for asset transfers. ↩
RGB++ - https://rgbpp.io - Enhanced RGB protocol with Nervos CKB integration. ↩
Sova - https://sova.io - Bitcoin Layer 2 with precompiled functions. ↩
THORChain - https://thorchain.org - Decentralized liquidity protocol connecting Bitcoin and other chains. ↩
Mezo - https://mezo.org - Bitcoin economic layer and appchain. ↩
Arch - https://arch.network - Application-specific Bitcoin Layer 2. ↩
Satoshi Protocol - https://satoshiprotocol.io - Bitcoin DeFi protocol. ↩
Kelly, K. (2010). What Technology Wants. Viking Press. On technology as an evolving system. ↩
Kelly, K. (2016). The Inevitable: Understanding the 12 Technological Forces That Will Shape Our Future. Viking Press. ↩