While open source software in general can be considered a huge success - most of the internet runs on it - games in particular were never really its strong suit. Sure, most classic card or board games like Solitaire, Chess, Go or Mahjongg have been implemented as open source apps and can for example be found in many linux distributions.
But what about modern, innovative games? Well, there’s Super Tux Kart a 3D racing game, Secret Maryo Chronicles - similarities with a certain italian plumber are completely coincidental - and the real time strategy game Warzone 2100.