I guess AGDS is owned by Future Games, the developer/publisher of Black Mirror and Nibiru, so perhaps you should contact them about licensing questions (
www.futuregames.cz ).
Otherwise you could take a look at the Wintermute-Engine (
www.dead-code.org ), as it has nearly all features AGDS has, and you can use it for free for non-commercial adventures. As far as I know it's the only free adventure-engine that supports realtime 3d characters like in Nibiru at the moment.