Shortly before I quit using OS-9 a GEM-like graphical user interface came out which was a precursor of what I later experienced using twm on Linux.I routinely ran 6-7 major applications at the same time(including a wordprocessor- Dynastar-a Worstar clone, a spreadsheet program-Dynacalc, a LOTUS-1-2-3 clone, and Dynabase, a DBASEII clone in addition a terminal for programming and other programs.