Darkside was the codename for the canned Sony Santa Monica game

Santa Monica (God of War) was developing a high budget product aside God of War franchise. Sadly, the game did not reach the minimum quality expectations to be commercialized, therefore the project was cancelled and the second unit of Santa Monica in charge for this game was dismantled.

Shinobi602, a well reputed insider, has added more info about this matter:

Darkside was definitely an interesting concept. RPG mechanics, customization, vehicles, post-apocalyptic open world…things just didn’t come together, milestone reviews failed. Trying to get that action-melee combat working with guns wasn’t easy.

An interesting game in the setting and the gameplay features, but apparently failed to mount all the pieces together.

Thanks, NeoGAF.