IBM wrote APL\360 in 360 assembly language. The IBM 5100 personal computer had a small cpu. They wanted APL on the 5100, so they implemented a 360 emulator and ran the original implementation of APL on that.
The XT/370 is particularly bonkers, as it uses a combo of a 68000 and an 8087 with custom microcode in them to run System 370 code.