[sahil-kang]

I believe at least some of the Linux maintainers use patchwork: http://jk.ozlabs.org/projects/patchwork/

[StillBored]

But patchwork is a pale comparison to many of the web based collaborative code review tools. Its basically a patch tracker plus some simple state tracking, rather than a full blown interactive communications tool.

[cryptonector]

And PostgreSQL has a thing called commitfest, which has some simple state tracking as well, with all discussion being based on mailing-lists.