You can download Gothic editor from world of gothic for example. Obviously some tools and documentation are in german, as are decompiled scripts included with it, but by now there are also english scripts available.
I guess we could keep exchaging game lists, but that was not really my point. An SDK, while in itself seemingly worthless to most people, would open door to a whole new dimension of Divinity - modding. Modding usually means strong fan communities, and that can only raise the worth of an intellectual property. If Larian would really want to add value to Divine Divinity and Divinity universe, releasing an sdk would be one of the chepest ways to do it. Unless of course parts of it contain licensed code.