According to me ReactOS need the subsystem: 1) Win98; 2) FreeDOS; 3) POSIX compatible (we don't need to run the same binary of linux, we can recompile it from sources); 4) GNUStep API (to have a MacOS X/Cocoa compatible API); 5) BeOS API. using dotgnu or mono we can have .net, and we can install a J...