The folks at Blockstream have been working on Simplicity for a long time. Simplicity launched on Liquid's mainnet earlier this year, but I hadn't seen the docs website they made for it before (linked above).
Simplicity is...a completely parallel alternative to [Bitcoin] Script....the language was designed to be able to express any finite function while avoiding the risks that come along with Turing completeness. No unbounded loops. No global state. These constraints are valuable to a developer who requires high confidence in the behavior of their application; with Simplicity, every possible outcome to the contract and its fee costs can be known before execution.
It is not coming to Bitcoin mainnet anytime soon (I believe it requires a fork and there's not been much discussion about it lately), but having it on Liquid means developers can try it out and see how it works.
If you'd like to learn more, check out their new docs page or here is a video about Simplicity from 2023