Mac OS X 10.0 (code named Cheetah) is the first major release of macOS, Apple's desktop and server operating system.

It was derived from NeXTSTEP and FreeBSD, and featured a new user interface called Aqua, as well as improved stability and security due to its new Unix foundations.

The release was met with mixed reviews, with some users praising the new features and stability, while others criticized the lack of compatibility with older Mac applications.

Some of the key features of Mac OS X 10.0 included the Aqua user interface, which introduced translucent menus, drop shadows, and other visual effects; the Dock, a new way of launching and switching between applications; and a new file system called HFS+.

The operating system also included built-in support for networking protocols such as TCP/IP and PPP, as well as for USB and FireWire devices.

[13] In the US, multiple Apple authorized resellers also held events on March 24–25, 2001, to coincide with Mac OS X's launch.

ZDNet called the new OS "underdone" due to poor performance, kernel panics, with main applications such as Finder causing system freezes.

[18] CNET rated Mac OS X 10.0, a 6 out of 10, calling it "more stable than previous Mac OSs", along with compliments on its UI, memory management and speed, but isn't "ready for the masses", due to issues such as the lack of native third-party applications for the platform, missing DVD playback and hard to use user interfaces.

[19] David Pogue stated in a New York Times tech column, that while he felt Mac OS X was better looking and easier to use than Mac OS 9 with superior features and menus, it is not yet ready for the average user, as it's not as polished, with missing features such as CD burning (at launch), automated shutdown scheduling, Labels menu.