I’ve just completed a project for the NYU Tisch School of Acting Graduate program Alumni Association or GAAA: http://gradactingalumni.org. I built a custom social networking application using the Symfony framework. I also created a plugin for WordPress that makes it user authentication system rely on the Symfony user login control.
With that in place it was relatively easy to get BbPress to integrate with WordPress since they are developed by the same group. There were a number of challenges getting all 3 application to work together and be able to access each others functions when necessary. I was also able to get the whole site layout to run off of WordPress’s template system.