Toolset

From NWNWiki

The Aurora Toolset is a powerful tool that is simple to use, which allows players to change almost any aspect of the game, create new modules using themed tilesets and turn any idea you may have into an in-game reality.

The Aurora Engine is actually an evolution of Infinity Engine which was used for the Baldur's Gate series of games. While the Aurora Engine is a huge leap, its base roots still stem from the Infinity Engine - all files types, the way the engine sorts data, etc. is the same.

Surprisingly, Baldur's Gate II had a wonderful modding community. They even went so far as to create their own toolset for editing the game. So, when Neverwinter Nights was released, it was a great gift to the Baldur's Gate II modding community and from that, Neverwinter Nights has flourished into what it is today.