A language for the .NET/Mono runtime with a syntax near identical to Python's.
See Gotchas for Python Users for specific comparisons between boo and CPython.
The main difference is that boo is statically typed with type inference. Syntax-wise it is like Python, but feature-wise it is also similar to C#. It implements many features that have been suggested for Python3.0, including a "with" statement and optional explicit static typing declarations ("x as int"). Extra features include anonymous methods/closures, custom macros and attributes (similar to PythonDecorators), and soon, optional case-insensitivity.
For resources on learning about the .NET standard libraries and 3rd party .NET libraries, see http://developers.coedit.net/DotNetProgramming