This may be of interest:

"Stackless Python allows you to use lightweight threads (tasklets) that can be switched with less overhead and it allows for cooperative multitasking with the intention of making async programming easier. This helps with IO bound applications where you can have tens of thousands of tasklets running at the same time (try doing that with threads). It does not however allow you to take advantage of multi-core or multi-processor resources. It simply allows you to squeeze the most amount of work out of a single threaded process..."

http://www.stackless.com/pipermail/stackless/2007-August/001...