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 the Debian infrastructure.

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

Ubuntu versions are named after various different animals, similar to how versions of Debian are named after various Toy Story characters.