This one is not all online, but it has an online and desktop component. Try Celtx at www.celtx.com. It is free and open source. I have not tried out the scheduling component but I know that it has one. If you sign up for an account and use the versioning system it should work for you.
I did a little video tutorial for a couple of guys that I share stuff with, not fancy but it may help. You can find it here:
http://www.screencast.com/t/GhbQcagb61
K