Today, Mac OS X today celebrates its 10th birthday. Apple introduced Mac OS X on March 24, 2001, a viable alternative to Windows for the average computer user.
One interesting part of OS X is the version system that Apple uses. Instead of incrementing each new release with an entire version number, such as from 10 to 11, each version of OS X is represented as 10.x.
The names of the operating system also have had a characteristic of being named after big cats, which in order of release are Cheetah, Puma, Jaguar, Panther, Tiger, Leopard, Snow Leopard, and the upcoming Lion.
Mac OS X 10.0 Codename "Cheetah" was the first release of the Mac OS X line of desktop and server operating systems released on March 24, 2001. It introduced as an upgrade to the "Classic" Mac OS 9.
Mac OS X 10.1 Codename "Puma" was released later in 2001 on September 25. This would also later become the first version of OS X to be included as the default operating system on new Macs in 2002 with the release of 10.1.2.
Mac OS X 10.2 Codename "Jaguar" was released on August 24 2002. OS X 10.2 was also the first in the line of operating systems to use its codename in marketing of the product. Upon boot users noticed a major change, where their beloved "Happy Mac" which had greeted them previously was now replaced with the current grey Apple logo.
Mac OS X 10.3 Codename "Panther" was released on October 24 2003. This release included many features that would change how people used the operating system, with many still in use and praised today. Apple finally retired the "pinstripe" theme, or at least put it at a minimum by introducing their "brushed-metal" interface that would be later replaced in Leopard with a more matte-grey.
Mac OS X 10.4 Codename "Tiger" publicly being available on April 29 2005. Tiger comes as one of the largest updates to OS X, including Spotlight, Dashboard, new versions of Safari and Mail, Automator, VoiceOver, Xcode 2 and an integrated Dictionary and Thesarus.
Mac OS X 10.5 Codename "Leopard" was released on October 26 2007. It was originally slated for earlier, however the brand new at-the-time iPhone was taking up much of the company's efforts.
Mac OS X 10.6 Codename "Snow Leopard" was released on August 28 2009. This version however is not geared for bunches of new end-user features, but rather optimizations of the core OS itself. Updates to Boot Camp, Finder, Preview, QuickTime, Safari, Time Machine, and VoiceOver are found, which mainly increases speed and compatibility while optimizing for the work done on the back end of Snow Leopard.
Mac OS X 10.7 Codename "Lion" recently introduced to to developers.