The Stable Channels Wallet lets users maintain a portion of their bitcoin as a synthetic dollar balance, all while staying self-custodial and 100% in bitcoin.

Stable channels website: https://stablechannels.com/

Guthub: https://github.com/toneloc/stable-channels

Here's a description of the idea:

Stable Channels ships as an iOS app, an Android app, and a desktop wallet (macOS, Windows, Linux). Every app runs a full Lightning node on the device and lets users stabilize the bitcoin that they send to themselves during onboarding.

The LSP/Server keeps the user stable by overcollateralizing the Stable Channel by 100% at the time of channel creation. Each user (the stability receiver and the LSP/stability provider) puts in the same amount of bitcoin, and the stability mechanism is activated.

The stability mechanism works like this: each node refreshes a multi-exchange BTC/USD price consensus every 15 seconds. Six direct USD markets are preferred; a geographically diverse BTC/USDT fallback is used only when at least three independent USDT/USD sources confirm that USDT remains within 0.5% of its dollar peg. At least three agreeing prices are required, outliers are excluded, and stale or suspicious prices can remain visible but cannot move money. Based on an accepted price, the nodes adjust the channel balance with their counterparty to keep the stability receiver's balance at a fixed dollar value (e.g., $100,000 of bitcoin).

I found a Summer of Bitcoin blog post about Stable Channels development that also had some explanation about the concept.

I haven't tested out the app yet, but it seems like a serious endeavor.