The stated goals of ReactOS are to be hardware and software compatible with Windows XP/Server 2003. ReactOS is also free, open source, and designed to be light and fast. It is designed to run on any CPU from an Intel 486 up to a Core i3/i5/i7 and to be compatible with serial, PS/2, and USB mice and keyboards. It also strives to support a long list of old video cards. 256 MB of RAM are recommended. ReactOS supports BIOS but not UEFI.
I tried it on an HP nc6320 a few years ago, and it installed, but I had problems with drivers. I tried the same model again about 6 months ago, and it didn't even boot this time :( I should try it again soon. It's a great project, it's just a shame that it feels like it's moving so slowly. It would be great as an alternative to old OSes like 2000 and XP that are no longer supported, but run expensive equipment like medical or other scientific devices.
A Brief Review of ReactOS
Qball wrote
It did not work last time I tried it. Maybe next one or in the next life.