App.net is a website/service that helps developers optimize their application’s online presence and provides tools to manage, monitor and promote their product. Using App.net, developers can create landing pages and widgets as well as monitor performance data. This is targeted towards developers who create cross platform apps and find it difficult to create a webpage for each one of those. App.net already supports iOS and Android OS, now its adding support for Windows Phone, Blackberry and HTML5 apps. You can see the above image as an example of the landing page that can be done using App.net.
Caldwell of App.net in an interview with VentureBeat says,
â€œA lot of the larger shops have apps on multiple platforms, and there are small developers that are experimenting with WP7,â€
More details can be found here and at app.net.