The .NET IL Interpreter
mattwarren.org
mattwarren.org
How it does types is interesting, and the GC is simple enough that it can be comprehended by mere mortals. I enjoyed my time playing around with it.
As a bonus, .NET MF is designed for production, and indeed it is used out in the wild!
Another one I've come across is 'DotNetAnywhere', see https://github.com/chrisdunelm/DotNetAnywhere