TitanPad is a collaborative document editor that requires no sign-up and multiple people can work on the same document simultaneously. The document gets updated and synchronized in real-time for all users.
You can export the edited document as a Word file, PDF, or an HTML web page. There’s a nice time-slider that replays your edits with time.
In addition to document editing, TitanPad can also be used for quickly transferring text from one mobile device to another – just open the same TitanPad URL on both devices, paste the text in one device and it will magically appear on other device.
TitanPad is based on EtherPad, an open-source project available on GitHub.
TypeWith.me is another good alternative to TitanPad.