Not to be negative here, but compare JRuby with IronRuby ... while IronRuby is basically unusable and almost dead, JRuby is not only really mature, but also the fastest Ruby implementation available. A lot of Ruby apps are right now deployed on top of Java servlet containers. There's practically no comparison to be made.

The only alternative language for .NET that's worth talking about is F#. But it's interesting to note that F# is sponsored and developed by Microsoft, while a language like Scala came from a third-party community. This is important because Microsoft is known to just dump projects that aren't generating a good return on investment.

     Java is now backed by Oracle which isn't the most friendly
     of open source companies either

Java was always backed by a huge community that includes IBM, Google, Intel, Red Hat, Novell and the Apache Foundation. The recent lawsuit against Google only goes to show that the genie is out of the bottle.

Actually Nemerle is a language worth talking about. What those guys are doing is brilliant. I remember even years ago - playing with the language - I was able to embed a natural syntax for a constraint programming library, encode a clean syntax on top of/for phantom types and write a monad system with transformers (via the macro system - think Lisp not C). This was back before Monads were cool in the regular community but very old hat in the haskell community.

What they are doing with version 2 is even more impressive and they are now sponsored by JetBrains.

F# is an excellent language* if you are doing Windows programming right now, you would be doing yourself a disservice not to look at it due to preoptimized worries. The language source is available , hacked on and ahead of Microsoft's version in certain aspects. In the case of a dumping, the community is talented and F# generates IL, unless C# is abandoned there is really nothing to worry about.

* I'm experimenting with intelligent, data based programming with a mix of Steffen Forkmann's JSON schema inference + ConceptNet + custom query syntax + embedded prolog + machine learning.

"unless C# is abandoned there is really nothing to worry about."

Hasn't Microsoft abandoned C# for internal development?

No. There was some FUD that because they didn't do things like rewriting Office in C# they weren't committed. Because rewriting 100 million lines of C++ just to prove a point would be such a good investment in time.

Major Products written substantially in C#:

SharePoint Visual Studio 2010 The C# compiler is being rewritten in C# Microsoft Dynamics