:-) I know what you mean about CP/M. I am not sure I've ever touched a Kaypro, though.

There are or were some alternative Z80 OSes: SymbOS, Cromix, Uzi/Fuzix, S-OS, DR's own MP/M... Not sure if any would run on a Kaypro without significant expansion, though.

Some of the early-1980s Forth environments were impressive. I read of a replacement ROM chip for the Sinclair ZX-81 which could handle multitasking and windowing.