*** NOTE: Python 3.3 only! This module is in the stdlib in Python 3.4. ***
On the heels of Python 3.4.0rc2, I've put a new version of the asyncio package for Python 3.3 on PyPI: https://pypi.python.org/pypi/asyncio/0.4.1
There's a source distro and a 32-bit Windows wheel. (For 64-bit Windows I could use some help.)
About asyncio: it's a new stdlib module for asynchronous I/O based on the "yield from" statement that was added to Python 3.3. It was inspired by Twisted and the async support in Tornado (amongst other influences). The original code name for the project is Tulip and this is where the latest developments happen: http://code.google.com/p/tulip/. Also check out PEP 3156: http://python.org/dev/peps/pep-3156/.
For Python 2 and 3.2, Victor Stinner has created a backport named Trollius: https://pypi.python.org/pypi/trollius/0.1.5