It is just amazing what this software can do. http://www.massivesoftware.com/what_massive.html
I first heard of it in the Special (Extended) Edition DVDs for Lord of the Rings. The software was actually built for those movies. Setting aside the movie and animation purpose, what stands out is how the AI operates.
There's no description of mine that could synthetise it better than these two paragraphs:
Even more amazing is the application for the game industry. Do please read about Massive Live. Once you set up an agent you can "play" against it with your joystick or gamepad. Everything from there on is completely calculated by the AI. You opponent can run and flee, get angry, scared, fight harder or fight for his life.Originally Posted by from their website
I understand this is a commercial application. But It's absolutely incredible the power of this AI. Just so that you have an idea, the two major battles in LotR (Helm's Deep and Pelennor Fields) where totally rendered with Massive on those long distance shots you see. Pelennor Fields had 350,000 agents on some of the shots.
I just wished to share this for those of you who could possibly not know about about it.
EDIT: Do check their showcase for amazing examples ofwhat can be done. Again abstract yourself from the rendering. What is amazing in this product is definitely the AI. What you are looking at is hundreds, thousands and tens of thousand individual agents each with it's own AI brain reacting nder crowd situations.