[NikkiA]

Early Mac Systems were written in pascal, well, Clascal as they called their Object Pascal system in those days, Clascal was developed internally at Apple with Wirth as a consultant. Think Pascal was the primary alternative to MPW until mid System 6 era. MacApp remained Apple's primary API until the mid 90s, and it was 100% written in Object Pascal (formerly Clascal).

Some chunks of Windows were also written in Pascal, using Microsoft Pascal which they'd been using since their CP/M days.

[eschaton]

They were not. The early Mac operating system and Toolbox were written in assembly, with a Pascal API. MacApp was ported to C++ in the late 1980s and went C++ only in the very early 1990s, about 1991-2 with MacApp 3.

MacApp was the framework Apple wrote and promoted, but it wasn’t the primary API; lots of developers wrote directly for the Mac Toolbox or used any of a number of other frameworks like THINK Class Library.

[kramerger]

This is very limited to mac, which was really tiny during that period.

The rest of the world looked very differently at that time, and compared to mac had much better development environment.