A quick inventory of major collaborative editor efforts, in chronological order.

As with any such list, it must start with an honorable mention to the mother of all demos during which Doug Engelbart presented what is basically an exhaustive list of all possible software written since 1968. This includes not only a collaborative editor, but graphics, programming and math editor.

Everything else after that demo is just a slower implementation to compensate for the acceleration of hardware.

Software gets slower faster than hardware gets faster. - Wirth's law

So without further ado, here is the list of notable collaborative editors that I could find. By "notable" i mean that they introduce a notable feature or implementation detail.

Project Date Platform Notes
SubEthaEdit 2003-2015? Mac-only first collaborative, real-time, multi-cursor editor I could find. An reverse-engineering attempt in Emacs failed to produce anything.
DocSynch 2004-2007 ? built on top of IRC!
Gobby 2005-now C, multi-platform first open, solid and reliable implementation and still around! The protocol ("libinfinoted") is notoriously hard to port to other editors (e.g. Rudel failed to implement this in Emacs). 0.7 release in jan 2017 adds possible python bindings that might improve this. Interesting plugins: autosave to disk.
Ethercalc 2005-now Web, Javascript First spreadsheet, along with Google docs
moonedit 2005-2008? ? Original website died. Other user's cursors visible and emulated keystrokes noises. Included a calculator and music sequencer!
synchroedit 2006-2007 ? First web app.
Inkscape 2007-2011 C++ First graphics editor with collaborative features backed by the "whiteboard" plugin built on top of Jabber, now defunct.
Abiword 2008-now C++ First word processor
Etherpad 2008-now Web First solid web app. Originally developped as a heavy Java app in 2008, acquired and opensourced by Google in 2009, then rewritten in Node.js in 2011. Widely used.
Wave 2009-2010 Web, Java Failed attempt at a grand protocol unification
CRDT 2011 Specification Standard for replicating a document's datastructure among different computers reliably.
Operational transform 2013 Specification Similar to CRDT, yet, well, different.
Floobits 2013-now ? Commercial, but opensource plugins for different editors
LibreOffice Online 2015-now Web free Google docs equivalent, now integrated in Nextcloud
HackMD 2015-now ? Commercial but opensource. Inspired by hackpad, which was bought up by Dropbox.
Cryptpad 2016-now web? spin-off of xwiki. encrypted, "zero-knowledge" on server
Prosemirror 2016-now Web, Node.JS "Tries to bridge the gap between Markdown text editing and classical WYSIWYG editors." Not really an editor, but something that can be used to build one.
Qill 2013-now Web, Node.JS Rich text editor, also javascript. Not sure it is really collaborative.
Teletype 2017-now WebRTC, Node.JS For the GitHub's Atom editor, introduces "portal" idea that makes guests follow what the host is doing across multiple docs. p2p with webRTC after visit to introduction server, CRDT based.
Tandem 2018-now Node.JS? Plugins for atom, vim, neovim, sublime... uses a relay to setup p2p connexions CRDT based. Dubious license issues were resolved thanks to the involvement of Debian developers, which makes it a promising standard to follow in the future.

Other lists

Google Docs
You're missing Google Docs, at least the word processor and spreadsheet programs support multi-edit.
Comment by Jonathan
Not Google Docs
Yeah no, I am not. I refer to it in the NextCloud section, but I generally tried to avoid proprietary software in there. If anything, I missed EtherCalc, created in 2005 basically at the time a similar product was acquired (not created!) by Google. So no cookie for them.
Comment by anarcat
comment 5
I’m not sure what editor is there in NextCloud, but LibreOffice Online is a multi-user editor and Google Docs alternative, so you may want to add or correct that entry.
Comment by Andrej Shadura
comment 6
Oh, I didn’t notice the link actually is to Collabora Online, which is a ‘branded’ version of LibreOffice Online. I think the entry should say LibreOffice Online or Collabora Online, not NextCloud, since it’s not something NextCloud itself provides, but an external piece of software.
Comment by Andrej Shadura
comment 7
AbiWord has supported collaborative editing since version 2.6 released in 2008.
Comment by Anonymous
keep em coming

Thanks for all the feedback! I've updated the table to add Ethercalc, Inkscape (how could I forget our poor Jabber friend!) and Abiword (that one still works??).

I've also fixed the "NextCloud" entry to be "LibreOffice Online" as, it's true, it's just one frontend. Plus it promotes it earlier in the history. Funny to notice that Abiword beat LibreOffice on that.. ;)

I've also added Google Wave, even though it was fairly short lived, in retrospect.

Thanks to the other suggestions, but the goal here is not to make an exhaustive inventory of all possible collaborative editors: there are way more than what's listed here. It seems that everyone thinks they can do better than whoever came before, so I tried to keep the list to project which brought something really new to the pool and/or that succeeded in a significant way. I also try to keep the list limited to free software project and open platforms, except when there is a really notable change.

Comment by anarcat
Collabora

I do believe it was Collabora who developed the 'online' part and released it first, and then contributed it back to LibreOffice which now also has it - credit-where-it-is-due would be to call it Collabora Online, I think.

Sadly the collaborative editing never made it into Kate proper...

Note that Abiword doesn't have a web view like Collabora/LibreOffice has, and LibreOffice still doesn't have collaborative editing on the desktop like Abiword has (but I believe work is happening to enable it).

There once upon a time was also the quite interesting Documents app for ownCloud/Nextcloud based on WebODF. It was a full javascript ODF editor that used the DOM tree, css etc to directly display and edit documents. So it had no import/export, it just directly loaded them and showed the documents in the browser! Quite clever, I don't think as of today any web editor can do that still). The biggest advantage was that the editor was non-destructive, even if it didn't understand or know how to display parts, they wouldn't get deleted/damaged on saving. There is a back-end for it that uses LibreOffice on the server to convert MS Word docs into ODF and back after editing, but, as that IS a destructive import/export, this has its limitations. https://github.com/nextcloud/documents

Sadly, while we kept it working with Nc 12 and will probably make it work with 13 someday, the actual engine is unmaintained so it won't be useful for much longer as browsers move on and break compatibility...

Comment by Jos Poortvliet
Created . Edited .