I haven't checked since the late 90s. What are they using? Just Git? Subversion or old school CVS/RCS?
Linux open source development:
10,000 lines are added the the linux kernel every day.
200 new developers every release
500+ companies involved
They can scale to these insane numbers because they don’t use github. Some good talks on this:
Discussion
They use git but you don’t need git to contribute. Patches are the lowest denominator.