The ReactOS® project is dedicated to making Free Software available to everyone by providing a ground-up implementation of a Microsoft Windows® XP compatible operating system. ReactOS aims to achieve complete binary compatibility with both applications and device drivers meant for NT and XP operating systems, by using a similar architecture and providing a complete and equivalent public interface.
Although Free Software advocates agree that free software operating systems improve the state of the art by fostering competition, ReactOS has practical benefit for others, too; ReactOS is the most complete working model of a Windows® like operating system available. Consequently, working programmers will learn a great deal by studying ReactOS source code and even participating in ReactOS development.
ReactOS components are growing more and more compatible with equivalent, closed source alternatives, but ReactOS doesn't simply stop at an arbitrary line in the sand. ReactOS has and will continue to incorporate new versions of the Win32 API and so will track and sometimes even define the state of the art in operating system technology. Rather than using current technology as a limit on our activities, we are constantly incorporating features from newer versions as well.
In short, ReactOS is aiming to run your applications and use your hardware! Finally, a FOSS operating system for everyone!