"Weta crowd supervisor Stephen Regelous has created
software, dubbed Massive, that creates realistic crowds. Every
individual in the crowd moves in response to stimulus such as
terrain, and to the actions of others.
The battles in The Return of the King will see hundreds of
thousands of these intelligent agents in frame at the same time, Mr
Labrie says, stretching the software to its limits.
Massive was developed on SGI operating system Irix and has since
been ported to open source operating system Linux."