https://github.com/Interlisp/medley Probably the closest thing to Genera which is FOSS and being actively maintained. Next closest thing would probably be Macintosh Common Lisp if you could run it under emulation. Besides that, idk, your best bet really would be just setting up Genera under VLM on Linux.
(And before you ask about the MIT CADR code dump, pretty much useless except from a historical POV. Same thing with LMI and TI Explorer system software)