Latest release of ReactOS 0.4.9, Installation and All Software. ReactOS is a free and open-source operating system based on the best design principles found in the Windows NT architecture. Written completely from scratch, ReactOS is not a Linux-based system and it shares none of the UNIX architecture. The main goal of the ReactOS project is to provide an operating system which is binary compatible with Windows. This will allow Windows applications and drivers to run as they would on a Windows system. Additionally, the look and feel of the Windows operating system is used, such that people accustomed to the familiar user interface of Windows would find using ReactOS straightforward. The ultimate goal of ReactOS is to allow people to use it as an alternative to Windows without the need to change software they are used to.