Collaborative writing software online with Writeboard. Write, share, revise, compare.
Picked this up via Ehub. From the folks who brought us Backpack comes a shared collaborative space. It looks like a basic text box, but contains some neat features that remind me of a basic wiki. In fact it shares a lot in common with a wiki, but it is more focused on text and collaboration.
Update: There is a pretty good review of Writeboard at Soultion Watch.