Concurrence: a Python framework to create massively concurrent network applications
opensource.hyves.org
opensource.hyves.org
Of that list, Concurrence is most like fibra and kamaelia, which also use python 2.5+ generators to achieve microthread concurrency.
If you want true concurrency of Python code (like if you wanted to run it on multiple cores at once), you'd have to use something like pyprocessing, which spawns off new processes instead of threads.
If you wanted, you could probably run as many separate python processes as you have cores. I doubt it would help that much, since the main bottleneck in this sort of application is usually the I/O involved in handling lots of small packets.
When Facebook made memcached multi-threaded (it's also based on libevent), things improved, but if I recall correctly, not that dramatically. They're probably getting more benefit out of it now that they've hacked the kernel to improve the packet/second bottleneck issues, but for most people that's probably not worth it.
As someone who really likes Erlang's approach to concurrency, I think it is very cool to see it starting to become available in more and more languages.
You can try to discipline yourself to use such a philosophy anyhow, but Python is going to be one of the worst places to try that. It is mutable to its core, which is one of the reasons it is cool, but doesn't lend itself to this approach very well.