Facebook's Hottest Games

Other applications, built by companies including Slide, Rock You! and Facebook itself, can boast larger numbers of total users. But Playfish is among the leaders in the stickiness game, outranking heftier competitors when it comes to engagement. Some 4% of Slide's installations are active on a daily basis, followed by Rock You!, at 2%, and many Facebook-made applications, at 1%.

That means Playfish applications ranks among the top five companies in total number of daily active users on Facebook--behind the likes of Slide, native Facebook applications (such as videos and notes) and Rock You!--but beats out its larger competitors when it comes to the ratio of daily users.

Founded by Glu Mobile veterans, Playfish views Facebook and other social networks as "the next generation of the game console," says de Halleux.

Companies like Playfish are also hoping to turn those repeat visitors into more lucrative customers. Ads, including video ads, will be part of that revenue stream. Playfish already boasts about its "TV-like" video ads that play at the end of game sessions, claiming its audience sticks around for the ad even though they don't have to.

But the most promising revenue strategy for such applications involves selling virtual items, says Jeremy Liew, managing director of Lightspeed Venture Partners and an investor in the application "Friends for Sale!" and the company, Rock You! Both Playfish, with "Pet Society," and Social Gaming Network, with "Warbook: Rise of the Infernals," are exploring virtual goods.

In Pictures: Facebook's 10 Hottest Games

"The initial signs are highly encouraging," says de Halleux. Players have an "emotional drive" to decorate virtual spaces and give gifts to friends in "Pet Society," a virtual pet-inhabited town. Playfish has even sold a few $40 lip-shaped couches, currently the most expensive item in the game.

Others are following suit. When Electronic Arts released "Scrabble" on Facebook in July, Chip Lange, general manager of EA's Hasbro Studio, told Forbes.com it would be the "most polished Facebook game that's ever been released."

Although "Scrabble" is flashy, it is has been plagued by bugs and has vexed hardcore Facebook aficionados who felt EA was trying to muscle out the independently developed "Scrabulous." Although "Scrabble" has scored a mere 297,684 installations, its users are active: As many as 32% of those who installed the game play it daily, according to Developer Analytics.

"We're in the 'Pong' stage of social games," says Shervin Pishevar, chief executive of Social Gaming Network (SGN). His company produced "Warbook," a virally powerful game. Building stickier games has been a tougher challenge so far.

SGN's "Space Movers" aims to raise funds to plant 10,000 to 50,000 trees in partnership with the Arbor Day Foundation, but so far the game has received a lackluster response from users. "We're investing a lot in ratcheting up the creativity to inspire people's imaginations to keep people coming back," asserts Pishevar. "The time spent [playing] is way higher, and return users is way higher than any other apps we've done in the past."

Describing the "first" and "second" waves of social network applications amuses Liew, who notes that all the work is still barely a year old. What he and other developers agree on, however, is that the newest generation of games--even "3.0 games"--will likely show up sooner on social networks than on the classic Web itself.

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