Off the top of my head: Twisted and gevent. It was actually the lack of a Python 3 gevent that lead my to create one crucial piece of software for my startup using NodeJs communicating with the main Python application passing messages via Redis.
Look, I'm a Python 3 supporter, but you should never foist the Python 3 fork of gevent on anyone.
I'm pretty sure that, the monkey-patched way most people use it, it's a happy accident when gevent even works correctly on Python 2. This happy accident doesn't happen in an unofficial fork.
