@WanWizard :
Or any other third party package you want to integrate into your application. We do something similar for third party packages in the core...
No ... is a general folder for external libraries, read better the previous WanWizard reply
This folder is used by the Fuel Parser package to add external parsers libraries ( like Smarty, Dwoo, Twig, .... ), take a look here :
https://github.com/fuel/parser