Most user-friendly collaborative editing way short of real-time?

Arguably, the most user-friendly way for multiple users to edit the same content is what google wave / google docs represents: Users see each-others' work in real-time.

What could next most known way on the user-friendliness scale, more offline way? There are some variants like locking, warnings of concurrent editing, showing both variants so the editor can manually merge, just plain overwrite the older... But is there something more friendly, in a way that at least (a) edits of the users will not be lost (b) live connection to the "master copy" is not required at all times?