We use Google Docs. It is not an easy process to do it, but once they year is set up it works pretty well. The plus side is that you can go back and see who made changes that were not requested (doesn’t happen too often).
As Sara said, we do ask that they sign up only a couple weeks in advance so that it is fair to all.
We have looked into other ways of doing it, but really have found nothing very good.
We have quite a few computer labs and carts here and i am one person responsible for scheduling them. Right now we use a giant paper calender per lab and it has worked out ok. Conflicts have arisen about who signed up for what period first and
people wanting to schedule from home, poor hand writing etc. Does anyone use technology to schedule labs or carts like a google spread sheet or calender or other means.