Facebook may be holding off on offering mobile app recommendations based on your friends’ tastes. But that isn’t stopping third-party developers from doing it on their own.

Vivek Agrawal and Shalin Mantri, who were behind a music app last year called Hitmaker, have built Apptitude — a way to learn about the mobile applications your Facebook friends use. It’s on a soft rollout now and has climbed the iTunes charts to #50 on the free app list today.

“The top 25 chart is essentially broken,” Mantri said. “It’s rigged and it’s unfair to independent app developers. We need to democratize the playing field for developers and more importantly, for users.”

Unlike other recently launched recommendation systems like Explor, the smart thing about Apptitude’s design is that it doesn’t require a user’s friends to have signed up for it. The app analyzes your friends’ previous Facebook wall postings to understand what mobile apps they might use. Basically, if a person’s friends have posted content on Facebook from a mobile app, that’s a sign that they’re an active user. It also detects whether a person’s friends have “liked” a mobile app’s Facebook page. That means the app doesn’t necessarily pick up every single app a person’s friend uses, but it does grab a number of them.

When you open the app, you’re presented with a top scrolling bar of your Facebook friends. If you pause on any individual friend, you can swipe through some of the mobile apps they use. Mantri and Agrawal also have plans to build in different game mechanics to reward users for finding hot apps first. The app is on a quiet roll-out now so it still has a few glitches to fix here and there, but overall it’s a promising approach.

Mobile app discovery is a notoriously difficult problem. While there are pay-per-install networks like Tapjoy where developers can buy enough downloads to propel them into the Top 25 of the iOS charts, there aren’t really great solutions for the long-tail of developers or for companies that don’t have the money to pay for downloads. Indie developers can get free credits from companies like Tapjoy, but they need to give exclusive distribution rights to them.

Other discovery solutions like Chomp, Appsfire and Appolicious have also come out in the last few years. But they tend to appeal to a minority of users who will go out of their way to search engines beyond the app store or voraciously consume articles and Top 10 Lists about apps they should use. Apptitude will probably suffer from this meta-discovery problem too.

To some extent, these discovery issues reflect deep cultural differences in the way Apple and Facebook have run their platforms over the last several years. Facebook has historically shied away from building app leaderboards, or prominently promoting its app directory, because it would prefer that users find apps through their friends. In contrast, Apple has never had social software ingrained into its culture; its iOS ecosystem has grown up and adapted to using leaderboards in the app store as a major distribution channel. These differences have created outward ripples in the way Apple and Facebook’s most powerful third-party developers design apps. Zynga has mastered the art of viral distribution. But on iOS, Rovio Mobile’s Angry Birds is barely social. And the truth is: it doesn’t need to be to get tens of millions of users.

We asked Facebook today about their plans for app recommendations while reporting on a separate story about their new mobile website. Unsurprisingly, they didn’t share much.

“We’re still chipping away at Facebook integration in third-party apps,” said Erick Tseng, the company’s head of mobile products. “The uptake of single sign-on [which lets users sign into new mobile apps once with Facebook] has been great so far. From all accounts, developers using Facebook have told us they’re seeing material benefits to growth and return engagement.”