Git

Git is a version control system for tracking changes in source code during software development. In the beginning there were many, some were licensed. As Linus worked on Linux one tried to strike him for using it without paying so he made git in 10 days as an F U. He made it because he needed it to work on the kernel with no one else in mind as the target audience. It’s since been maintained by Junio Hamano and became nearly the only version control system used by anyone in software.