Cafe.com, a social network for game playing, has opened its previously invite-only platform to all developers.

While most of the attention in the social games space is focused on bringing games to existing social networks (mainly Facebook), Cafe.com is going the opposite way by creating a social network entirely dedicated to playing free online games. The company is now competing for developer attention with the big social networks like Facebook and MySpace, but unlike these platforms, Cafe.com supports multiplayer gaming. This may turn out to be its ace-in-the-hole. Neither Facebook nor MySpace have multiplayer game support and, as a result, real-time games have failed to take hold on those sites.

But Cafe.com is not the only company attempting to be a social network built around online games. Kongregate, a popular flash game portal, has many social elements (and $8 million dollars in investment from Greylock Partners and Bezos Expeditions). Big Fish Games, a casual gaming site that also incorporates many social networking features, recently raised $83 million.

To further attract game developers to its Open Bar development platform, Cafe.com claims to provide “write once, play anywhere” capability. Games developed for Cafe.com, in other words, can be launched on other social networking platforms without additional coding. A similar claim is being made by J2play, a Canadian company that recently won a grant from fbFund, a fund setup by Facebook to encourage innovative apps. Cafe.com has 25 development studios enrolled in its Open Bar program.

Roman Nouzareth, CEO of Cafe.com’s parent company, Boonty, says that while most of his competitors focus on providing simple things like leaderboards, the Open Bar platform provides access to a full range of multiplayer game development tools. These include avatars, virtual items, achievement badges and presence management, which lets players know when others are available to play.

Nouzareth won’t disclose Cafe.com’s user numbers, but says they are greater than the 50,000 visitors reported by Compete. When I went to the site, it had about 1,820 users playing. Nouzareth does say that 82 percent of the site’s visitors are women, that the age range is 25 to 45 and that 52 percent are playing multiplayer games.

Looking at Google Trends, it appears that Cafe.com’s largest audience is in Asia, specifically the Philippines, which explains why its most popular game is Temple of Mahjong: Mahjong is to middle-aged Filipino woman what Texas Holdem Poker is to American frat boys.

Author Bret Terrill covers the social gaming space daily on his blog Bret On Social Games