The Facebook API library provided by Facebook is notoriously huge in source code at least, and they're pretty proud of the size of it, can't find the link right now, but they had a blog post talking about it a few years ago ago.
Here's a link to the oft-mocked slides from the talk where a Facebook engineer spoke about how iOS can't handle the scale of their app because they do the very logical thing of using over 18,000 classes: https://www.columbia.edu/~ng2573/zuggybuggy_is_2scale4ios.pd...
