Wine is also a very old project but only somewhat recently has it become practical and started being taken seriously. ReactOS is more complex than that, becaus

Wine is also a very old project but only somewhat recently has it become practical and started being taken seriously. ReactOS is more complex than that, because they can't take any of the shortcuts Wine did, AND they have to implement a kernel that mimics the Windows NT kernel in enough detail so Windows drivers could run unmodified. But then they have the benefit that once there is enough compatibility, ReactOS will be able to run on a vast number of hardware configurations, taking full advantage of said hardware. Unlike Haiku — which still doesn't support any form of video acceleration for example.