ReactOS is a free, open-source Windows NT-like operating system for both 32-bit and 64-bit personal computers, originally developed in 1996. It maintains system-level compatibility with Windows (including computer programs and device drivers developed for Windows Server 2003 and later versions of Windows), and is committed to becoming a perfect replacement for the Windows NT series.

The ever most widely used and important operating system was Windows 98. Its predecessor is Windows 95, which is a direct successor to Microsoft's prior standalone operating systems MS-DOS and Windows 3.1. As a major milestone of Microsoft's operating system, many of the classic features and designs that Windows 95 first introduced, such as the Start Menu, My Computer, as well as the classic card game - FreeCell, are still in use today.