title: Opensource or libraries for implementing marketplace or app store
body: <p>I'm going to implement a web-based marketplace for digital contents.
  Somehow its features are similar to app store where selling items are apps but my marketplace targets are digital contents.
  Before I begin implmenting everything from scratch, I want to make sure that I don't reinvent some wheels. Any recommended tools or personal experience is welcome. Scalability is my main concern for tool adoption.</p>