The standard Python interpreter also supports an interactive mode in which it acts as a kind of shell: expressions can be entered one at a time, and the result of their evaluation is seen immediately. This is a boon for those learning the language and experienced developers alike: snippets of code can be tested in interactive mode before integrating them into a proper program. As well, the Python shell is often used to interactively perform system tasks, such as modifying files.
Python also includes a unit testing framework for creating exhaustive test suites. While static typing aficionados see this as a replacement for a static type-checking system, Python programmers largely do not share this view.
Standard Python does not support continuations, and according to Guido van Rossum, never will. However, better support for coroutine-like functionality is planned, by extending Python's generators 
- Python – The reference implementation, also known as CPython
- Jython – Python coded in Java
IronPython – Python for .NET and Mono platforms
- Boo – Python-based but with static typing, for .NET and Mono
- Stackless Python - Python with coroutines
- Psyco - not an implementation, but JIT compiler for CPython
PyPy – Python coded in Python
- Parrot – Virtual machine being developed mainly as the runtime for Perl 6, but with the intent to also support dynamic languages like Python, Ruby, Tcl, etc. Can currently execute a subset of Python
- Logix – Python alternate front-end with macros
- Movable Python- An alternative distribution of CPython for Windows. It can run off a USB stick and provides a Portable Programming Environment.