Yeah, it's languished for years. I did a stint last autumn to get it to start passing more of Rubyspec, but haven't had time to take it further.
github.com/vidarh/writing-a-compiler-in-ruby
It's self-hosting apart from the GC (which is a sore spot - I really want to rewrite the GC in Ruby too), glibc for a handful of functions and syscalls, and using gas/ld to assemble and link.