ReactOS? is an advanced free open source operating system 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.
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 has and will continue to incorporating features from newer versions and sometimes even define the state of the art in operating system technology.
In short, ReactOS is aiming to run your applications and use your hardware, a free operating system for everyone!
Please bear in mind that ReactOS 0.3.1 is still in alpha stage, meaning it is not feature complete and is not recommended for everyday use.
Overall :- Its fine and have iso file sizing about +- 15 MB (at the time of writing). You must try it and see the difference . its free so why not try it . setup in 5 min max.
Bottomline :- Hangs tooo many time . My opinion is that you should not use it as a primary OS as it is in alpha/beta stage.
See their official webpage at http://www.reactos.org/en/index.html