Atari is developing a user-created online social world, upping the number of upcoming virtual worlds emphasizing user-developed content to eleven, according to GigaOM (via MCV).

Atari is joining an already overflowing roster that includes Sony’s Home, Viacom’s as-yet-unnamed world, along with start-ups Areae, Croquet, HiPiHi, Kaneva, Multiverse, Ogoglio, Outback Online, and Whirled. (A guide to these burgeoning virtual worlds can be found here.)

GigaOM thinks the rash of user-generated virtual worlds comes from game publishers slowly learning to apply the logic of Web 2.0 in their own medium.

Creating content is expensive and involves an increasingly futile struggle to retain subscribers. Traditional online worlds require a large team of designers and artists constantly adding new content, for fear that players will quickly churn through the existing experiences, get bored, and leave. Going the user-created route means new content on a regular basis, produced by subscribers, with the company only spending money to foster and police it.