This summer we told you about Detour, the new company from Groupon founder Andrew Mason dedicated to creating high-quality audio tours. After several months in private beta, Detour is now open to the public: you can download the iPhone app today. (An Android app is forthcoming.) Open it and you'll find seven tours of San Francisco, each focused on a different neighborhood or topic, narrated by different experts in the topic. In our tests, we found the app to be a fascinating guide to the city, with tours that play like particularly sharp episodes of This American Life.

You can pay $4.99 for an individual tour, or $20 for an annual subscription that gets you access to everything. Tours cover neighborhoods including the Tenderloin, the Marina, Union Square, and Fisherman's Wharf. A new tour will come out about once a month, Mason says.

Unlike Groupon, rocketed to a $6 billion valuation, Detour is poised for slow growth: it's a media company as much as it's a technology company, and for now its product is available in a single city. But more are coming: Detour has partnered with popular radio show and podcast Radiolab to create a tour of Austin, TX, that will be available in time for the South by Southwest festival next month.

You can download Detour here.