Microsoft Flight Simulator (often abbreviated as MSFS or FS) is a series of applications for Microsoft Windows amateur flight simulator, as well as previous applications for MS-DOS and Classic Mac OS. It is one of the longest-running, most popular, and most complete programs on the market. It was the first product in the Microsoft app portfolio and is very different from other Microsoft software, which focuses on business. At 37 years old, is a long-term software product line, which preceded Windows by three years. Microsoft Flight Simulator may be the longest PC game series ever.