Brad Abrams mentions at the Rotor BOF session mentions that Rotor (a free, fully functional implementation of the ECMA #335 standard for a common language infrastructure.) has moved from a skunkworks projects to being fully managed by the CLR team.  When code is checked into the CLR there are tests that determine whether it might break anything  in the Rotor Unix build.  They are looking to release a Whidbey version of Rotor after Whidbey has shipped (someone mentioned September 2004).  Other points:

• There's also a community site at http://sscli.net 
• There's a rotor list at the developmentor site.
• Intel does stuff with Rotor (some of the guys were in the session)
• It's focussed on academic, non-commercial use.  For acedemics and those that are interested in getting under the covers and understanding how .NET works.  The license forbids re-releasing or using it in a commercial product.
• I know a lot of people who use it to run the CLR on Mac OS X
• It's popular with grad students working on Rotor for thesis topics like garbage collection tuning.
• It's for people who want to 'fix' who the CLR, for example Chris Sells got some research funding to look at deterministic finalization.

Brad Abrams wanted to know whether anyone was interested in using the JIT compiler and making it available in the Rotor distribution - you couldn't modify it but it would allow for better performance.

It's interesting to see this effort from Microsoft based on building a community of interested people.  Quotes: 'If you blog it they will come'