Looks like some people still maintain CMUCL. > I thought SBCL was its considered its successor. Generally SBCL has a lot of advantages, incl. being available

Looks like some people still maintain CMUCL. > I thought SBCL was its considered its successor. Generally SBCL has a lot of advantages, incl. being available on current 64bit platforms. The typical developer will very likely better use SBCL. It's not unusual though that some out-of-fashion Lisp implementations are still maintained by a small group - as long as there is enough knowhow available. Clozure CL for example currently has the problem that some people would like to use it, but it has not the necessary maintainer with the needed low-level knowhow. A problem is for example to get a native port to the Apple Silicon Macs done. Something which was done for SBCL quite some time ago.