When it comes to the business of app distribution, the current battleground is incentivised downloads.

This typically sees users rewarded with virtual currency for a game they're playing if they download games and apps offered other publishers.

Mediating this exchange are companies such as Tapjoy, which practically invented the mobile form of the business when it was trying to monetise its TapDefense iPhone game in 2008.

Since then it's built out its infrastructure, handling around 1.5 million app downloads daily across iOS and Android. In total, it's logged 200 million unique devices globally, and boasts that with 500 advertisers live on the system at any time, its fillrate is 99 percent.

Money for nothing

It's an enviable situation, and one many companies - both from the games and app markets - are looking to muscle into.

For example, Flurry has launched a similar service called AppCircle, and companies such as MdotM and G6 Pay are also active in the space. Game distribution networks such as Free App A Day are looking to expand their activity too.

"It's a large market and we have first mover advantage, but we welcome competition. It's good for advertisers, publishers and consumers," says Deng-Kai Chen, Tapjoy's senior product manager for mobile.

All along the watchtower

Certainly, the scope of incentivisation is changing fast.

"We're seeing new ad types developing all the time," says Chen. "For example, our new Pay Per Action model enables publishers to incentivise people to download their game and say, play the tutorial or complete level 3."

It's a situation that, in some ways, could seem counterproductive as it results in publishers effectively paying people to play their games.

Chen doesn't see an issue however, as long as Tapjoy's users remain in control of their actions.

"We're not forcing users to do anything," he explains.

"Tapjoy presents them with a small subset of the App Store or Android Market and we incentivise them to try out a game. The deal is 'We'll give you some virtual currency to try out this game'. The most important thing we focus on is providing them with a good user experience."

Cake for all

He also thinks the market is expanding so quickly - both in terms of new freemium game releases and new smartphone owners - that there's more than enough to go round for publishers using the Tapjoy system to push their apps.

"When it comes to casual mobile gaming, I really don't think there's competition over eyeballs. The market is growing so fast, and we're seeing people playing multiple titles at the same time. There's a large enough pie for everyone," he says.