Bizarre Creations' colourful multi-directional shooter Geometry Wars was never intended to be a game at all. It began life as software the studio was using in-house to test the Xbox controller during the making of Project Gotham Racing 2.
Employees had a lot of fun with the programme, and they felt the public would too, so they sneaked a modified version of it into the racing game as an unlockable Easter egg. They had no way of knowing it would become a phenomenon in its own right.
Many Project Gotham Racing 2 fans spent as much time whittling away the hours in this hidden mini-game as they did on the in-game tracks, and this prompted Bizarre Creations to give Geometry Wars a standalone release.
At one point, the game held the record for most downloads on Xbox Live, and has gone on to spawn a series and a wave of imitators, such as the PC clone GridWars.