[mbell]

I would say that CPython, PyPy and Stackless are in pretty strong competition in different areas. PyPy only supporting 2.x seems to be a relatively unimportant metric given the slow adoption of 3.x. As for it being experimental, perhaps technically but I do believe its used in production in many places. From what I know Stackless gets a large portion of its support from CCP games due to its use in Eve Online. I'm sure there are others but its use case is relatively unique.

[stcredzero]

In the grand scheme of things, the differences between CPython and PyPy are minor. Stackless is a special case. Relatively Python has very little language fragmentation. It has more of what I'd call "implementation fragmentation," but not too much of that either.