ReactOS: Open Source Windows OS

ReactOS is an open-source operating system designed to run Windows applications and drivers without containing Microsoft code. The project, running since 1996, uses clean room reverse engineering to achieve Windows NT compatibility. Version 0.4.15 shows significant improvements in stability and application compatibility, successfully running software like Microsoft Office XP, Adobe Audition, and Blender. While still in alpha with hardware compatibility limitations and occasional crashes, ReactOS demonstrates potential as a niche solution for running legacy Windows software in open-source environments, particularly when deployed in virtual machines.