Source control systems, also known as version control systems, store code and other static files, such as images, with a history of the changes made to those files.
Git is a free and open source distributed version control system.
Mercurial is similar to Git, also a free and open source distributed version control system.
GitHub is currently the most commonly used source control platform for using Git.
BitBucket provides free Git and Mercurial repositories for open projects and private repositories for up to five users. Users pay for hosting private repositories with more than five users.
Staging Servers, Source Control & Deploy Workflows, And Other Stuff Nobody Teaches You (Patrick McKenzie)