ReactOS [L1 ] is a GPL 2 license operating system that aims to replace Microsoft Windows 98, Windows 2000, and their successors.
Internally, it makes use of Wine libraries. Externally, it has a general look and UI similar to Windows XP in "classic" mode.
peterc 2008-06-10: While general system stability is a serious issue in version 0.3.4, my starpack applications ran on it without any serious problems, apart from some alpha transparency issues with some PNG icons in Tile buttons.
It's promising in that by the time it is a stable platform in a couple of years (say, in 2010), it will be in competition with Windows 7 without MinWin to stem the Vista bloat. ReactOS may be an easier sell to IT departments at this time than official Microsoft Windows.