Piranha Bytes worked more than 4 years on the development of Gothic's technology. The engine was created completely in-house, with a modified version later used for Gothic II. These are the only games to use this engine. The Engine's Codename is ZenGin, because of the *.zen file technology.
A comprehensive entry level guide on the most basic task to execute in the ZenGin games' environment: adding an item to the game (in this case it's Uriziel from Gothic, to Night of the Raven). Updated link for clean scripts and some typos fixes.