http://www.qubeos.com

"Qube is the first multiplatform desktop environment. Currently, it supports three of the most popular operating systems all over the world such as Linux, Windows and DOS. Application based and compiled for Qube environment run without need of recompiling on all of supported platforms in the level of machine codes. This means an application compiled for Qube will run on all supported platforms at maximum speed and minimal hardware requirements. Qube supports multitasking for all applications running under it."