Remember GEM? No? GEM (Graphical Environment Manager) was the first GUI for the PC. It was written by Digital Research and released in 1983. (MS Windows 1.0 was released on Nov 1985.) GEM has been GPL’ed and, surprisingly, continues to live.
Links:
Google
GEM, a Mac-like GUI and OS for Low-end PCs
DeltaSoft
GEM Workshop
GEM World
OpenGEM
Intel GEM
GEM Programs