It’s a way to get developers into the MicroSoft world, there’s also been a big push recently with open source projects, and some are doing very well, like TypeScript. From what I recall Freetrade are using TypeScript as well, TypeScript is a superset of JavaScript with type checking.
It’ll be interesting to see what happens to the Atom editor maintained by GitHub as MicroSoft have one that directly competes with that.
GitHub has some big names relying on GitHub Enterprise, so there’ll be opportunities to cross sell: