Memory Pool System
Provide MPS as alternative backend for garbage collecting. Authors are willing to provide alternative licenses for FOSS projects (at least that was a case with CLASP).
pros:
1) multiple kinds of arenas, each with different GC strategies
2) the moving compacting GC can to auto-pinning
cons:
1) FFI becomes somewhat challenging, unless you maintain a
completely separate C and lisp heap
-- auto-pinning makes it easy