Etherpad

Real-time collaborative text editing where several people type in the same document at once, and every keystroke is synced between browsers as it happens. The editor tracks authorship per change, supports revisions and time travel to earlier states, and takes plugins for chat, imports, and exports, so it can serve as a full document editor or a small component inside another application.

Communities use it for meeting minutes, shared drafts, and paired writing on internal wikis.

Hosting it yourself keeps draft documents and edit history on your own machines, and the data is plain text that moves easily.