I've been building a pretty complex scheduling system for work, and although it's been designed with our requirements in mind I believe it is general enough to be useful in plenty of places.
Essentially it's a combination of perl classes, a daemon and a database backend, which provides various ways to schedule tasks:
The system is kind of peer to peer, in that there is no master node, only the database itself, which all the nodes access.
So is it just me - or is that pretty useful?
Naturally it has a seperate web gui to manage it, built using Maypole.