Seems like you are looking for an App Store for SaaS apps, like the Chrome Web Store, but more general purpose and less Chrome specific.

Edit: as much as I despise the term, Social App Store. You would need algorithms like Pandora uses, that tracks how often and for how long a user uses certain kinds of apps, and through categorization, tailor a "Recommended" page to popular apps in the same category, as well as ones that "friends" use on a regular basis.