Facebook open source apps?

Question

Facebook

Hello.
It became interesting to see if there are ready-made large applications for Facebook (and social networks in general) with published source codes. Preferably games with the implementation of the server and client parts.
And offtopic: even if such applications exist, it is quite obvious that opening source codes for applications for social networks is not common among developers. With what it can be connected (besides strictly commercial orientation)?
PS As an example, the Ruby RPG engine is FreeRPGEngine , but I would like to see Python or PHP.