Galactic Arms Race (GAR) is a multiplayer online game that also serves as a "research experiment in automatic content generation driven by player preferences," that they describe as "'Space Diablo', with real-time combat, cool particle system weapons, and RPG-style leveling and skill trees" (thanks Mike Martinez and Slashdot). The website has videos and write-ups describing how systems within the game evolve, and since there's a new version 1.1 this forum thread outlines what's new and different. Here's word on the game:

Unique game content, namely spaceship weapon systems, automatically evolves based on player behavior through a specialized version of the NEAT evolutionary algorithm called cgNEAT (content-generating NeuroEvolution of Augmenting Topologies). In particular, new variants of weapons that players like will be continually created by the game itself. In this way, the game never stays the same. GAR is the first video game to demonstrate that critical content can evolve as the game is played to satisfy its players.