React Operating System
ReactOS® is a free, modern operating system based on the design of Windows® XP/2003. Written completely from scratch, it aims to follow the Windows-NT® architecture designed by Microsoft from the hardware level right through to the application level. This is not a Linux based system, and shares none of the unix architecture.
ReactOS® is an effort to create a Free Software replacement for Microsoft Windows® that is compatible with existing hardware and software!
The ReactOS operating system design is able to provide portability across families of processors, such as Intel x86 and even provide portability across different processor architectures, such as CISC and RISC. There is only one single OS core, the kernel; porting ReactOS to other architectures only involves porting the hardware abstraction layer, the lowest part that talks directly with the platform hardware.