I use klisp[1] and bronze-age-lisp[2] mostly for testing, as they're the closest to a feature complete implementation of the Kernel Report.

I've written a number of less complete interpreters over the years. I currently have a long-running side-project to provide a more complete, highly optimized implementation for x86_64.

[1]:https://github.com/dbohdan/klisp

[2]:https://github.com/ghosthamlet/bronze-age-lisp