When Kiip announced its $4 million round of funding last week, we were wondering what new could be added to the mobile advertising table if it wasn’t incentivized installs, classic mobile banner or interstitials ads or branded virtual goods.

But Kiip’s take is very novel indeed. The San Francisco based mobile advertising network gives gamers real-world rewards when they hit certain achievements in a game. Companies like group deals startup Homerun.com can offer free goods from local businesses while Sephora can give make-up samples to gamers when they level up. The company has rounded up other big brands like popchips, Sony Dash, Vitamin Water, 1-800-Flowers, Dr. Pepper, GNC, Carl’s Jr and Hardee’s.

It’s a nice way to capitalize on the psychological boost a gamer gets when they unlock a new item or level up.

“This is one of those ideas that’s naturally very sticky. People will slap their foreheads and wonder why this doesn’t exist already,” co-founder Brian Wong tells us. “But it’s very difficult to find people who buy ads who aren’t fixated on impressions. This is the result of seven months of hard work and thinking.”

The ad network is out in 15 games today, which reach about 12 million monthly active users. Wong isn’t saying which games because he’s concerned that people might go to the games directly for the rewards, which will interfere with some of the late-stage tweaking the company wants to do.

For advertisers, Kiip is based on a cost-per-action model: they pay between 25 cents and $3 whenever a user signs up for a reward.

Kiip doesn’t pass on any identifiable user information like an e-mail address to the advertiser. The targeting works like any other ad network where the advertiser can specify location, gender or device type, for example. Wong wouldn’t say exactly how he gets that demographic info but a lot of it does come from the game developer.

Integration is pretty similar to how other ad networks function. Developers add a few lines of code to drop in Kiip’s SDK. Android and iOS are ready to go; Kiip isn’t aggressively pursuing other mobile platforms at this point. There are also frequency caps to make sure Kiip isn’t showing too many rewards or the same ones over and over to players.

Kiip: An Introduction from kiip on Vimeo.

Kiip: A Welcome from kiip on Vimeo.