Mine is Scheme for Max, now on it's fourth open source release, but really written so I could make computer music how I want to. It's an extension to the popular Max/MSP visual music programming environment that embeds an s7 Scheme interpreter and provides a substantial API/FFI to Max. It allows you to script Max (and thus also Ableton Live) with Scheme, enabling interactive coding, algorithmic music, live coding, macros, and just much more pleasant scripting than in JavaScript. It locks in with the scheduler so you can even use Scheme powered sequencers within Ableton Live alongside regular Live tracks, and you can build sophisticated Live control surfaces using the Live API.
Github page here: https://github.com/iainctduncan/scheme-for-max
YouTube demos here: https://www.youtube.com/c/musicwithlisp
A recent demo of it in the context of Live is this one. https://www.youtube.com/watch?v=j0sKBA-Pv2c&t=1s&ab_channel=...