Git, the open source distributed version control system created by Linus Torvalds to handle Linux's decentralized development model, is being used for a rather surprising project: Windows.
Traditionally, Microsoft's software has used a version control system called Source Depot. This is proprietary and internal to Microsoft; it's believed to be a customized version of the commercial Perforce version control system, tailored for Microsoft's larger-than-average size. Over the years, Redmond has also developed its own version control products. Long ago, the company had a thing called SourceSafe, which was reputationally the moral equivalent to tossing all your precious source code in a trash can and then setting it on fire thanks to the system's propensity to corrupt its database. In the modern era, the Team Foundation Server (TFS) application lifecycle management (ALM) system offered Team Foundation Version Control (TFVC), a much more robust, scalable version control system built around a centralized model.