I know the folks at Overleaf and they're awesome! However, their editor is not open source. But yes, ShareLaTex probably needs a spot on there, though I haven't looked at it in a long while and it seems to be pretty dormant in terms of development: https://github.com/sharelatex/sharelatex/graphs/contributors
Had no idea it had real-time collaboration... Wonder how it's done. Digging in now... :)
If you're using it, it would be great to get your thoughts on it and what particular things you like about it.
Update: ShareLaTeX uses a string-based collaboration algorithm (i.e. LaTeX is plain text, not a structured document format), and seems to be limited to max 2 collaborators (though that could be old info), so that explains why it didn't appear on my radar. I'll take it for a spin anyway, thanks!
Also, you might be unaware of CoCalc, which is open source https://github.com/sagemathinc/cocalc. CoCalc supports collaborative editing of many structured documents, including Jupyter notebooks, but not rich text at present.
Just to be clear, open source development of ShareLaTeX is ongoing and indeed has accelerated since Overleaf and ShareLaTeX joined forces. ShareLaTeX is split into many repos, and the one linked above is a 'coordinator' repo that doesn't get updated much. See https://github.com/sharelatex/web-sharelatex for one that is more active.
The free version of Overleaf/ShareLaTeX does have a restriction on the number of collaborators: you plus one other. Paid accounts support more collaborators [1], and you can also get more collaborators on the free account by referring others [2].
