We are currently working on the development of a common platform for all of our applications.
The first element of our platform is PHPartials. It is an application development library that provides all common functionality needed in (social) web applications. On the lower level it contains user management, authorization, search, data abstraction, caching, API and feed generation and payment handing. On the higher level it has user profiles, groups, file management, photo and video sharing, social networking, forums, social bookmarking, comments, tagging and more.
We are currently using PHPartials as part of multiple projects, for example: