WordPress can become anything you want it to be, with the right amount of good code - a social network, a freelance website, an online store, etc. the sky is the limit. So ultimately, WordPress is just a fantastic platform and with the right tools and knowledge you build almost anything on top of it.

We are more limited if we are not allowed to change anything in WordPress, but keep it as is, out of the box. This is an important restriction for the discussion, I think, as otherwise we can go on forever, naming ANYTHING that can be built online using WordPress.

We've seen even Integrated Game Development Environments in WordPress, remember back in 2011? http://2011.toronto.wordcamp.org/session/using-wordpress-to-build-interactive-games/ Toronto WordCamp? Again, the sky's the limit.