The App Discovery beta feature is only available on StumbleUpon's Android app, which already helps users discover new websites. It recommends Android applications based on what websites the user has liked via StumbleUpon's interface, the user's app preferences (after you log in with your StumbleUpon ID, it asks you if it can take a look at your existing apps), as well as his or her friends' app usage. It also looks for apps that are usually downloaded in combination with others. Suggestions are displayed one by one (including descriptions, screenshots, and Android Market star ratings) for you to vote up or down. A recommended app can then be downloaded straight from the Android Marketplace.
Given that the iOS store has over 300,000 apps and the Android Marketplace has more than 100,000, this is a great initiative by StumbleUpon. There's a lot of noise, and it can be hard for mobile developers to increase exposure for their app, and is subsequently hard for consumers to find what they want. StumbleUpon said the Android Market was its first target because it's particularly poorly organized for users who want to do more than keyword searches, and it was also faster to develop in terms of both the actual building as well as the approval process. An iOS version is in the works, but the timing question remains unanswered.
StumbleUpon was founded in November 2001 by Garrett Camp, Geoff Smith, Justin LaFrance and Eric Boyd in Calgary, Canada. It launched in 2002 and didn't move to the San Francisco Bay Area until 2006. It was acquired by eBay a year later for $75 million.