Five implementations of the Python language are in active development:
- CPython is the most widely used implementation and is often called just Python. CPython is the implementation that gets all the latest features first. Its current version is 2.6 for the 2.x series and 3.1.* for the 3.x series.
- Stackless Python is a variant of CPython that supports multithreaded programming with less overhead per thread than CPython. It currently supports Python 2.6.5 for 2.x and 3.1.1 for 3.x.
- Jython, formerly known as JPython, is a reimplementation of Python in Java. It can seamlessly use Python and Java together in a single program. Jython currently supports Python 2.5.
- IronPython runs atop Microsoft's .NET Common Language Runtime, and can integrate with the C# language in much the way that Jython integrates with Java. IronPython currently supports Python 2.6.
- Pynie runs atop the Parrot Virtual Machine and can integrate with Perl 6 and there is support being built for over twenty new languages.
- PyPy is Python implemented in a subset of Python itself.
The list of implementations at the official CPython site also names Python for .NET (a distinct project from IronPython) and Vyper. Both of these projects seem to be abandoned, and indeed the Sourceforge project page for Vyper has disappeared.