7. Gutsy Gibbon (7.10)
Flickr image credit: superwebdeveloper
Found in tropical and subtropical rainforests, Gibbons are apes in the family Hylobatidae. They're also cute, and they bond in pairs just like we do. Swinging from branch to branch at speeds as high as 35 miles per hour, they are reportedly the fastest and most agile of all tree-dwelling, non-flying mammals, according to Wikipedia.
And what of Gutsy Gibbon? Well, released in October 2007, it's perhaps best known for adding AppArmor for security, fast desktop search and a graphical configuration tool for X.Org. Compiz Fusion was also enabled by default.