mc4p (short for Minecraft Portable Protocol-Parsing Proxy) is a Minecraft proxy server. With mc4p, you can create programs (mc4p plugins) that examine and modify messages sent between the Minecraft client and server without writing any multi-threaded or network-related code.
To install from source, just clone the GitHub repository. You can then install it in 'development' mode with
python setup.py develop
If mc4p is installed in 'development' mode, you can uninstall it with
python setup.py develop --uninstall
mc4p is licensed under the Do What The Fuck You Want To Public License, Version 2, as published by Sam Hocevar