This is a bugfix release for 2.2 - but some small new features were added, too. Removed civilian death limit. Instead you will lose if you make too many nations unhappy. Improved in-game IRC client. Added UFO Theory to Tech Tree. UFO: Al
UFO: Alien Invasion has released 2.3.1. This release is a bug fix for the stable 2.3 release and maintains compatibility for all saved games under 2.3. It includes dozens of fixes to small bugs throughout the game.