My experience has shown if I want something in Java, I can usually find it from a source I think is reputable for stability and serving large numbers of customers: Apache, Codehaus, JBoss etc.
If I want something in Ruby, I throw my chips in with some guy on GitHub (who was nice enough to pack it as a gem), usually choose based on whether it was good enough to at least come with half-decent documentation.
I wouldn't necessarily agree that JS or non-Apple Obj-C libraries are all that much better than the Rails community effort though.
There is something to be said for the amazing contributions the Apache group has made to open source. I pick Java mainly to benefit from their brilliance (I suppose I could use Scala, Groovy, etc. instead though).
If I want something in Ruby, I throw my chips in with some guy on GitHub (who was nice enough to pack it as a gem), usually choose based on whether it was good enough to at least come with half-decent documentation.
I wouldn't necessarily agree that JS or non-Apple Obj-C libraries are all that much better than the Rails community effort though.