Far be it for me to disagree, but I have a few differing opinions...
Production-ready and in active development:
Matz' Ruby Interpreter (MRI) / CRuby: <
http://Ruby-Lang.Org/>
I personally wouldn't consider MRI (i.e. 1.8 series) as being under
"active development". It's basically feature-frozen (for some definition
of "feature freeze" and development efforts are focusing almost
exclusively on the 1.9/2.0 line.
Production ready for some things, at least
I think even the Ruby.NET guys would say it's a bit of a stretch to call
it production-ready.
In active development, but not necessarily production-ready:
Yet Another Ruby VM (YARV): <
http://WWW.AtDot.Net/yarv/>
YARV is probably more production ready than anything but MRI (and maybe
JRuby), but there's of course a lot more work planned before official
release as Ruby 1.9.1 and 2.0
No disagreement. Somewhat less "active" than JRuby, Ruby.NET, or
Rubinius, but making excellent progress all the same.
As far as I know Cardinal is not under active development right now.
Maybe when Kevin Tew finishes up the Parrot dev tasks he's working on now?
Other than JRuby, there's probably more folks actively working on or
contributing to Rubinius than any other impl on this list. "Very" active
development?
Dead, as far as I've heard. Wilco doesn't have time to work on it anymore.
Died in the crib...I'm not sure any work was ever really done.
Could see new life through Rubinius and JRuby reusing what's been done,
but I don't think there's been any progress in a looong time. I'm
seriously looking at using some of MetaRuby in JRuby very soon though.
There's also a potential implementation coming directly out of
Microsoft, though we won't know for sure until they make an announcement
of some kind.
- Charlie