Collaborative Writing

How do you collaborate with others on real academic writing (e.g. proposals, journal articles, book chapters, etc.)? The typical academic collaboration involves sending around a MS Word document and using Track Changes to track everyone's edits and comments. But there are some really intriguing tools out there allowing multiple authors to edit and format an online document at the same time.

1. Google Docs is obvious and many colleges and universities are switching to Google Apps for Education and away from Microsoft.
2. writeLaTeX/Overleaf is build on LaTeX and popular with the mathematics, physical science, and engineering crowd.
3. Authorea and The "Paper" of the Future.
4. Fidus Writer is the open-source alternative.

All those work really well in combination with an online lab notebook such as Beaker, Projects, or IPython.