BeOS had pervasive multithreading and a slick UI. The BeBox had dual CPUs, a novelty at the time and many years before multi-core CPUs.
Linux was still very new, and didn't have much of a GUI at all (maybe basic X, but this was long before Gnome, KDE, Englightment, etc)
Mac System 7 didn't have protected memory or preemptive multitasking.
Windows 95 was brand new and while a big improvement over Windows 3.1, was still very prone to crashing.