They have their own in-house version of just about every dev tool. http://phabricator.org/

FYI phabricator originated at Facebook, but the guys who wrote it left and founded Phalicity, who supports it full time now. Facebook did the world a service by open sourcing phabricator.

Review board and Gerrit are both awful in comparison

I've been using Phabricator for a few months now, and I used Gerrit for over 2 years at my last job.

They each have their strengths, but both of them are infinitely preferable to not doing code review. Neither is awful.

This might be right in spirit, but Phabricator is maintained by Phacility (some ex-FB people) and used by at least 6 other companies outside of FB.

That's one way to keep your talent from being poached :)

If you are at the point where you are contemplating building your own dev-tool-everythings... then you've gone very wrong. Let the dev-tool guys make dev-tools, they are much better at it (it's all they do). Instead figure out how to make them work in your business environment. Facebook may have one of the largest sites on the web, and perhaps the most users... but their codebase itself is nothing special and does not warrant "special" tools. That's just BS and a measuring contest.

To be fair once you are over 1000 engineers, a 1% improvement in productivity is worth a lot of development time.

Somehow Netflix never got that memo and they seem to be doing just fine.