Mac OS X Cheetah

Mac OS X Cheetah, or Mac OS X 10.0, is the first retail release of Mac OS X, which was released on 24 March 2001.

Main changes
This is the first release of macOS which is based on the new Darwin kernel, making features possible which were not available in previous releases such as cooperative multitasking.

The new dock simplifies management of applications compared to the MultiFinder from the Classic line.

Criticism
While being praised for the features listed above, Mac OS X Cheetah was initially a subject of criticism, as it did not have as many features as compared to Mac OS 9. Also, even after Apple published the Cocoa API for hybrid Mac OS 9/X applications, many applications were not ready for Mac OS X and only could run under the Classic environment. In addition, older Macintosh computers performed slower on Mac OS X than on Mac OS 9.

Many of these issues were fixed with later versions of Mac OS X.