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!