Windhoek is the code name of a DDE-based hard disk driver. Built as a prototype in 2008, it only supports IDE. It should probably be adapted to use libATA for real use.
Being incomplete, Windhoek is not part of the public L4Env release. The current version can be downloaded however: http://os.inf.tu-dresden.de/~doebel/downloads/windhoek.tar.bz2.