I'm not sure what a "Preliminary Beta" is but QIT has released a one for their Ruby.NET compiler. They expect to achieve "full semantic compatibility" (can you tell this is an acidemic project?) by the end of the year. Thanks to David Ing for the link.
They claim to "pass all 871 tests in the samples/test.rb installation test suite of Ruby 1.8.2." which seems odd since later they say "We have a plan for how to deal with continuations but we have not yet implemented them." Doesn't the Ruby test suite test continuations? I wish they would provide more details on this plan, continuations might not be the most interesting thing in Ruby, but it's up there and it's probably the hardest thing to implement on top of the CLR.
BTW, there are two other projects @ QIT that Ruby.NET leverages that look interesting. The Gardens Point Parser Generator is essentially a YACC clone written in C# and making extensive use of generics. Personally, I'm more interested in Parsing Expression Grammars, but there's no C# implementation as of yet. QIT also has a library for reading and writing program executable files (i.e. EXEs and DLLs).
As a quick aside, I'm getting pretty tired of all the different euphemisms for "alpha". In the age of perpetual beta, isn't alpha the new beta? But everyone seems worried about calling their releases alpha as if it means "it might not cause your machine to explode, if you could actually get it to compile". So we end up with things like "Preliminary Beta" and "Community Tech Preview". We all KNOW what these terms mean, so lets just call an alpha and alpha, shall we?