Keep in mind that the Mac Plus CPU was something like an 8 MHz 68000. I don’t think a 486 was ever clocked that low?

Apple used MPW internally for Mac development by ≈1986, as others have noted. MPW was a Unix-like environment. However, the MPW toolchain was much slower to compile and link.

In any case, by the 486 era, a serious developer would have wanted to run a 68030-based Mac at minimum, which would have been a similar experience to this video, but much faster and often on a larger screen.