You can say whatever you want about Facebook, but their tool/system for committing code changes is sheer perfection. Starting with managing source code changes

You can say whatever you want about Facebook, but their tool/system for committing code changes is sheer perfection. Starting with managing source code changes on your own dev server, getting it code reviewed, merging it into the main branch, and getting it deployed to production. All of it is easy to figure out, and it works without complications. It can handle pull requests of 20000 files without any trouble.