Nothing more than an Operating System, that runs in Protected Mode and supports Multi-tasking and Multi-threading, with a nice GUI (sort of) + some basic drivers and Apps....
NOTE: It's out-of-date, the new version will be released soon.
FreeOS/1 is a Free, Open Source, FreeDOS based Free and Open Source Alternative OS, with open source Microsoft Windows compatibility using HXDOSExtender KernelEx,and ReactOS source code. FreeOS/1 will include new technologies and will be easy to use