Mac OS X V10.0
Mac OS X version 10.0, code named "Cheetah", is the first major release of Mac OS X, Apple’s desktop and server operating system. Mac OS X v10.0 was released on March 24, 2001 for a price of US$129. It was the successor of the Mac OS X Public Beta and the predecessor of Mac OS X v10.1.
Mac OS X v10.0 was a radical departure from the previous “classic” Macintosh operating system and was Apple’s long awaited answer to the call for a next generation Macintosh operating system. It introduced a brand new code base completely separate from Mac OS 9's, as well as all previous Apple operating systems. Mac OS X introduced the new Darwin Unix-like core and a totally new system of memory management. It proved to be a rocky start to the Mac OS X line, plagued with missing features and performance issues, although it was praised for being a good start to an operating system still in its infancy, in terms of completeness and overall operating system stability. Unlike later releases of Mac OS X, the cat-themed code name was not used in marketing the new operating system.
Read more about Mac OS X V10.0: System Requirements, Features, Limitations, Criticisms, Multilingual Snags, Release History