Here is the timeline histroy of Apple's Mac OS X operating system, this article and image is taken from git-tower website.
Cheetah : 03 / 2001 – OS X 10.0)The history of OS X started with a bear, not a cat: in September of 2000, Apple presented Kodiak. For 30$, users could purchase this first public Beta of Mac OS 10. The official OS 10.0, Cheetah, followed 6 months later. It featured Apple's brand new user interface Aqua and the first versions of apps like TextEdit, Preview, Mail, and QuickTime. The new OS X demanded an (at that time: whopping!) 128 MB of RAM and 800 MB of disk space.
Puma : 09 / 2001 – OS X 10.1Just half a year later, Puma was released. Instead of delivering many new features, it focused on improving the system's performance. With Mac OS 10.1.2, Apple also started shipping OS X by default with new computers - and replaced OS 9 for good.
Jaguar : 08 / 2002 – OS X 10.2
Panther : 10 / 2003 – OS X 10.3
Additionally, Apple presented Exposé to improve working with multiple open applications.
Tiger : 04 / 2005 – OS X 10.4
Tiger brought the invaluable Spotlight search to Mac OS. It was also the first version to present Widgets (like a calculator, a calendar, or a clock) on the new Dashboard. Besides that, Mac OS 10.4 inaugurated new hardware: it was installed both on the first Macs with Intel processors and on the first Apple TV devices (that were yet to come out later, in 2007).
Leopard : 10 / 2007 – OS X 10.5
The new Leopard, anyhow, introduced a built-in backup system called Time Machine. It also brought full support for 64-bit applications. Moreover, Mac computers could now run other operating systems like Microsoft Windows - thanks to Boot Camp.
Snow Leopard : 08 / 2009 – OS X 10.6
Lion : 07 / 2011 – OS X 10.7
Mountain Lion : 07 / 2012 – OS X 10.8
Mavericks : 10 / 2013 – OS X 10.9
Yosemite : 10 / 2014 – OS X 10.10