Boo is a Python-flavored language for .NET and Mono. It is statically typed, but has a “duck” type similar to the dynamic keyword in C# 4.0. It is compiled, but has strong meta-programming capabilities. Using Boo feels like using a more indie version of C#. It doesn’t have the tools support that C# has, so many .NET programmers have never heard of it, but it does a lot of interesting things that the mainstream languages aren’t doing yet.
These are some of my favorite features with examples. Some are just nice-to-haves, others change the way I think about coding in Boo versus C#.
Concise, Implicitly-Typed Variable Declaration
Concise Arrays (With Unpacking!)
Syntactic Macros + Quasi-Quotation
If any of that looks interesting to you, I encourage you to try it out. MonoDevelop ships with an add-in that makes it easy to get started, the language itself is open source on Github with very helpful test cases documenting the more obscure features, and there’s an active mailing list to help answer your questions.