A few AOT attempts as well, including mine (I've hardly touched mine in the last couple of years, but I have a bunch of GC improvements that haven't been pushed to GitHub that brings it close to self-compiling, but still huge gaps - e.g. no float or regex support, no exceptions)
- DragonRuby - I don't know if it should count separately form MacRuby
- There were at least 5 Ruby-to-JavaScript compilers I remember from about 10 years ago, but they are very hard to find. Surprisingly, one of them - ruby2js - is still alive and actively developed!
- 2 Rubinius attempts (Gnu Lightning and LLVM)
- MacRuby
- JRuby (do you count InDy separately?)
- IronRuby (do you count DLR separately? They didn't start with DLR, as far as I recall)
- MagLev - I think they hoped to GemStone would JIT user's Ruby code with bits of interpreter.
- TruffleRuby
- RubyOMR
- Vladimir's MJIT
- Koichi's MJIT
- YJIT
Do we count HotRuby and Opal? - both compile to JS.
I miss a few.
EDIT: mRuby, duh