SubEthaEdit style networked editing

[Shug Boabby]

Hi everyone,

I have used a program named SubEthaEdit in the past for collaborative
editing of a text file. One computer is designated as the server for
the file, then other users can connect and edit the file... everyone
sees everyone else's edits in realtime in their editor (in different
colours).

This is the most incredible collaborative editing tool I have ever
seen, with only two problems... it is only for the Mac and, most
importantly, it is not Emacs.

Does anyone know of any Emacs packages that accomplish the same thing?
Or has Emacs hit a dead-end in its ability to be extended?