Boo
   New object-oriented statically typed language for Common Language Infrastructure (.NET, Mono), Python inspired syntax, focus on language and compiler extensibility.
   http://boo.codehaus.org/

CPython
   The original implementation of Python, written in C.
   http://python.org/download/

IronPython
   A fast Python implementation for .NET and Mono.
   http://www.codeplex.com/Wiki/View.aspx?ProjectName=IronPython

Jython
   A 100 % Pure Java implementation of the Python language.
   http://sourceforge.net/projects/jython/

PyPy
   Development of a highly flexible Python implementation.
   http://codespeak.net/pypy/

Python for .NET
   Package gives nearly seamless integration with .NET Common Language Runtime: CLR. Strong scripting tool, allows scripting or building full programs in Python, using .NET services and components coded in any language targeting CLR: Managed C++, C#, VB, JSc
   http://pythonnet.sourceforge.net/

Stackless Python
   An experimental implementation that supports continuations, generators, microthreads, and coroutines.
   http://www.stackless.com/