JRuby is a wonderful project. But it's boring to use. It just works, and the java integration is painless (ruby calling java) or basically trivial (java calling ruby).
It's got quite a velocity of development, which is really promising for the future.
It's not completely pure Java though. The distribution includes a few JNI .so files for the odd bit of integration, but they've hidden pre-compiled versions for most platforms so it's unzip and go like java libraries.
I can see how that's ambiguous. I mean this in a totally good way. Moving to a new implementation of a language interpreter should not have any exciting surprises, it should just behave in the same way as any other implementation.
JRuby succeeds remarkably well in working exactly as the MRI implementation. Therefore I consider "boring" to be high praise.
What's exciting is what it enables, which is real threading and java integration. But that's another story, and I do intend to write a blog post on it soon.
It's got quite a velocity of development, which is really promising for the future.
It's not completely pure Java though. The distribution includes a few JNI .so files for the odd bit of integration, but they've hidden pre-compiled versions for most platforms so it's unzip and go like java libraries.