Ubuntu

Ubuntu is a distribution of Linux that was started in 2004. Unlike many other Linux distributions, Ubuntu is designed for use as a desktop OS and currently owns the 3rd largest market share on OSes.

The Ubuntu system is built on Debian in infrastructure.

Version history
Ubuntu is versioned differently to other software, with a main version indicating year of release and subversion indicating month, so if it was released in September 2007 it is version 7.09 and in December 2013 it is version 13.12. The first version was 4.10 (October 2004). Here is list:

4.10 - Warty Warthog (released on 2004-10-20, support ended on 2006-04-30) 5.04 - Hoary Hedgehog (released on 2005-04-08) 5.10 - Breezy Badger (released on 2005-10-13) 6.04 (LTS) - renamed to 6.06 6.06 (LTS) - Dapper Drake (released on 2006-06-01) 6.10 - Edgy Eft (released on 2006-10-26) 7.04 - Feisty Fawn (released on 2007-04-19) 7.10 - Gutsy Gibbon (released on 2007-10-18) 8.04 (LTS) - Hardy Heron (released on 2008-04-24) 8.10 - Intrepid Ibex (released on 2008-10-30) 9.04 - Jaunty Jackalope (released on 2009-04-23) 9.10 - Karmic Koala (released on 2009-10-29) 10.04 (LTS) - Lucid Lynx (released on 2010-04-29) 10.10 - Maverick Meerkat (released on 2010-10-10) 11.04 - Natty Narwhal (released on 2011-04-28) 11.10 - Oneiric Ocelot (released on 2011-10-13) 12.04 (LTS) - Precise Pangolin (released on 2012-04-26) 12.10 - Quantal Quetzal (released on 2012-10-18) 13.04 - Raring Ringtail (released on 2013-04-25) 13.10 - Saucy Salamander (released on 2013-10-17) 14.04 (LTS) - Trusty Tahr (released on 2014-04-17) 14.10 - Utopic Unicorn (released on 2014-10-23) 15.04 - Vivid Vervet (currently in alpha) (scheduled to be released on 2015-04-23)