I've been evaluating ShareDB[1] for a Google Docs-like and it seems promising.

The OT space is really interesting. For those wanting to read more about it, check out the paper: "Operational transformation in real-time group editors: issues, algorithms, and achievements"[2]

[1] https://github.com/share/sharedb

[2] http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.53....