Smartphone owners are willing to download up to 100 apps, but only use around 15 per week. That’s out of the 700,000 apps in the iOS app store. The odds of breaking into that exclusive group of 15 go-to apps are very, very low.

In his roles as a developer at TapWalk, Sean Casto repeatedly went through the heartache of building and abandoning apps that failed to catch on. So he built a marketplace to connect app lovers with newly launched apps to help them get the early traction they need. It’s called PreApps.

But don’t call it an app discovery platform. There are plenty of those, and they lack the most important element of any marketplace: buyers. PreApps will populate its site with app enthusiasts through partnerships with popular app blogs,” Casto says. Those partnerships are still in the works, so this whole thing is fairly hypothetical at the moment. But you get the idea.

The marketplace approach makes sense: PreApps is connecting app lovers with app makers. The Web works best when it’s a marketplace, Twitter founder Ev Williams said last night at a Branch-hosted roundtable discussion. The beauty of products like Twitter, Facebook Instagram, or Tumblr was their built-in audiences. This was one of the biggest problems with his first company, blogging CMS Blogger, or WordPress now. There was no built-in way to accumulate a guaranteed audience, nor was there a way to get much passive feedback. Content creators would feel frustrated and abandon their blogs.

Facebook succeeds in part because it is a marketplace for “Likes.” Instagram is a marketplace for little hearts. Twitter is a marketplace for links (and witticisms, he added).

PreApps builds an audience for an app before it’s even prepared to launch. Its audience can browse through apps that are in the works and click a button to be alerted when the apps are available to the public. This is extra special for alien Android users like myself who are now accustomed to waiting months to be able to use the apps they read about every day.

Developers can use PreApps for free, but there are a handful of premium features they can upgrade to. Paying developers can survey PreApp’s audience on various features or the appearance of their apps. They can pay to get promotional placement on the PreApps page. They can learn about app development, tips for submitting to the App store and Google Play, and connect with app developers and logo creation services.

Further, PreApps will have a crowdsourced app contest to choose a popular app idea among its audience members. The winning idea actually gets built. This is great, because every time I tell someone about my day job, I get pitched on their hairbrained idea for an app. (“Why isn’t there an app that tells me the gender of my baby?” “I have an idea for an app that’s like Instagram… but for words.”) From now on, I’ll send them to PreApps, where the crowd can shoot down their ideas (or not! Instagram for Words may have the last filter-tinged laugh on me).

Everyone has an app idea. Now, with such a low cost to build an app, everyone has an app. Cutting through the noise will always be a huge problem; PreApps just wants to help. The site follows its own best practices of building up buzz, pre-launch. It’s not officially available until November.