Earlier this week, Facebook announced the fbFund, which will provide grants to companies and individuals interested in building applications for the social-networking website. (See “Facebook Funds Developers.”) The move seems intended to encourage programmers to make applications that are more sophisticated than the bulk of what’s already been created by third-party developers. Some companies could find themselves scrambling to roll with the new order.

When Facebook launched Platform, a system designed to let programmers create applications for users of Facebook, the market was glutted with quick, simple applications built to grow. For example, Extended Info, an application that expanded Facebook users’ ability to list information about themselves, won the Red Bull Flight Experience Award in July for garnering the most users in the month after Platform launched. “My application is simply an upgraded, obvious feature that was only successful because Facebook, for whatever reason, chose not to do it themselves,” says Trey Philips, the developer of Extended Info. Facebook continues to offer its own apps as well, but Philips points out that any move the company makes will likely compete with a third-party application.

Philips recently set off a buzz in the blogosphere when he discovered hints in Facebook’s API that seem to suggest that the company plans to add a function that could allow users to customize their lists of friends. If added, the function could directly compete with Slide’s Top Friends application, which has more than 15 million installed users on Facebook, according to Adonomics, a site that tracks Facebook application statistics. (A Facebook spokesperson says that the company does not comment on future product plans and declined to be interviewed for this story.) Philips notes that Facebook can only avoid competing with its developers by coming up with truly unique ideas or by limiting itself to releasing an application, such as one for chat within Facebook, that uses the site in ways that developers can’t.

Facebook has already added functions that enhance its wall–a bulletin board on a user’s profile page–in ways similar to enhancements made by applications such as RockYou’s Super Wall. “It’s totally within Facebook’s power to go out and expand their scope into the territory of [other] platform developers,” RockYou CTO and cofounder Jia Shen says. “It’s not like I’ve received a message [stating that] they’re specifically gunning for our application. I think they’re taking a lot of pointers from our applications.” Shen says that RockYou has kept Super Wall popular by continuing to add functions beyond those provided by Facebook, such as the ability to leave graffiti-style messages on Super Wall.

Jesse Farmer, who created Adonomics, says that developers shouldn’t be surprised if they collide with Facebook. Applications that piggyback on existing features are naturally at risk of becoming irrelevant, he says. Of deeper concern to developers, he believes, is Facebook’s recent change to its metrics, implemented at the end of August, which he thinks suggests the direction the company wants application developers to take. “This last metrics change made them all a little nervous,” Farmer says.

For the first few months of Facebook’s Platform, the company ranked applications based on the number of users who had installed the application. The new metrics give a number of daily active users, along with a percentage that seems to represent the daily active users in comparison with the installed user base. The change cut numbers dramatically. Super Wall, for example, was previously listed as having more than eight million total users, and now it shows up with only 800,000 daily active users. Meanwhile, extremely simple games such as Zombies and Pirates vs. Ninjas were forced to adapt to the metrics switch by adding functionality to their existing viral design.

“We were primarily focused on overall user numbers, originally,” says RockYou’s Shen. But he says that moving to the new model has been good for the company’s products because it has forced him and his colleagues to focus on making their products more interesting to use, instead of just easy to share.

But while the metrics change makes sense on the surface, Farmer says, “nobody except Facebook really knows what those numbers mean.” He says that he hasn’t been able to determine what qualifies a user as active. For example, he says, when someone posts a photo to Super Wall, it’s not clear whether that is being counted as a single action or as an action on the part of every person who receives the post.

Regardless, Super Wall is a fiercely viral application. “Whenever we’re going to develop new functionality into an application, we think about what you’re going to do as a specific person, and how that triggers actions from all of your friends,” Shen says. When a user posts a drawing to Super Wall, he says, the application makes it very easy to share that post with all the user’s friends. This aggressive strategy to keep users engaged seems to be keeping developers like RockYou and Slide on top for now. The developers make money by including ads in their applications and by helping other developers make their applications more viral, for a fee. For example, Yahoo recently enlisted RockYou to help market its struggling music-video application.

B.J. Fogg, who directs research at Stanford University’s Persuasive Technology Lab and will be coteaching a class on Facebook applications, says that the fast pace of Facebook application developments suggests a new model for how interactive systems will be made in the future. “I think one of the things to explore is consumers writing their own interactive applications that they would then share with their social network,” Fogg says. “Facebook users wrote code to answer their own needs–Extended Info and Top Friends and Super Poke–and created stuff for themselves. And that might be the model of how interactive experiences are created in the future.”