Autonomous Character is a behavioral animation plugin by Montreal-based BioGraphic Technologies that allows animators to create natural-looking animations of large groups of interacting intelligent characters, such as F1 drivers passing at high speeds, sharks hunting schools of fish, or Roman legions crushing hordes of barbarians (see gallery). The autonomous character’s personality is created according to a rich set of behaviours such as pursuing other characters, following paths, joining groups and avoiding obstacles. Highlights include fast results for pre-visualization of animations with large numbers of characters, possible interaction of behaviors with dynamics (*) and the ability to leverage the results for game development via a SDK (offered separately). Autonomous Character has been recently released for Maya and a Max version is in the works: contact BioGraphic if you're interested in participating in their beta program.
Also of note, BioGraphic founder Paul Kruszewski has been co-developer of previous plugins such as Tree Druid and Thor.

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Features:
(the following correspond to the Maya version of the plugin, the features of the Max version may vary)
       Rich palette of movement behaviours
            Individual behaviours (Seek, Flee, Pursue, Evade, Arrive, AvoidBarriers, AvoidObstacles, Wander,
            FollowPath, FollowFlowField)
            Group behaviours (Separate, Approach, Align, Flock)
            Hybrid behaviours (FollowLeader, HuntPrey, EvadeHunter)
       Easy to use states and transitions (e.g., AmFlighting, AmDying)
       Realistic Environments
            2D & 3D solvers
            Surface hugging
            Collision detection
       Artist-centric
            Fully integrated into 3D program's UI
            No programming required, all behaviours are create via plug-in interface
            Supports scripting
            Builds on the “Art to Engine” pipeline.  Export results to any game engine that supports the BGT’s
            Autonomous Character Engine SDK.
       High performance
            Real time feedback
            cache

Price for the Maya version of the plugin is $999.00 US.

BioGraphic Technologies also offers a middleware "Autonomous Character Engine":

The Autonomous Character Engine (ACE) Software Development Kit (SDK) is a middleware solution that allows interactive content developers (e.g., video game developers) to quickly and effectively add advanced artificial intelligence (AI) technology to their engines in order to create richer, more interactive and intelligent characters.  This “Brain in a Box” solution integrates seamlessly into advanced art-to-engine solutions that rely on advanced 3D content creation tools as their level editors.   The creative power of ACE can be harnessed either by an artist-centric visual interface or directly by its powerful programming SDK.