So, let's see. There's

• CPython
• Jython
• IronPython
• PyPy
• Starkiller
• Something on Parrot
• Something on Smalltalk VM
• Stackless (which is a kind of a different implementation) and
• Psyco (which is a kind of a JIT compiler for Python)

Any others? (There used to be an implementation of Python named Vyper, but it no longer exists.)

I wouldn't complain about Python having too few independent implementations anymore.