This was brought to my attention last night and I thought it could be an interesting way to scale bitcoin today.
Spark is an off-chain scaling solution that builds on top of Statechains to enable instant, extremely low fee, and unlimited self-custodial transactions of Bitcoin and tokens while also natively enabling sending and receiving via Lightning.
Spark is not a rollup, nor a blockchain. There are no smart contracts nor VM. Spark is native to Bitcoin and its payments-focused architecture, enabling on-chain funds to be transacted at any scale, with near-instant speeds, and at virtually zero cost.
It took me by surprise as I always thought that Spark were working on LN. I believe they are a service provider for Coinbase. I'm sure there must a catch when something seems too good to be true.