Go To Locomotion System
From the website:
Take a look at how semi-procedural animation can dramatically improve the realism of animated humans and animals.
Full Control of Style
Animators are experts in creating motions with specific styles and personalities. The Locomotion System uses keyframed or motion-captured animations as input and only adjusts them minimally to move the feet correctly in a dynamic and detailed environment.
Full Control of Behavior
Move your character around by any means you desire, be it a CharacterController, a RigidBody, or your own custom movement logic. The Locomotion System simply observes the position, alignment, velocity and rotational velocity of your character and deduces everything from that, along with some raycasts onto the ground.
The Locomotion System automatically blends your keyframed or motion-captured walk and run cycles and then adjusts the movements of the bones in the legs to ensure that the feet step correctly on the ground. The system can adjust animations made for a specific speed and direction on a plain surface to any speed, direction, and curvature, on any surface, including arbitrary steps and slopes.
The Locomotion System is available for free commercial and non-commercial use when used in a Unity game.
The full license is included in the package.
The Locomotion System is developed by Rune Skovbo Johansen in collaboration with Unity Technologies.
The presentation of the Locomotion System at Unite 2008 was received very well judging from the number of times the audience burst spontaneously into applause, and this Gamasutra article refers to the presentation as a "crowd favorite". I'll let you know when the video of the presentation is online.
If you are a Unity user and have any technical questions regarding the Locomotion System, please ask them on the Unity forums so more people can benefit from the questions and answers (and maybe notify me by email of your forum post if you want to be sure I see it quickly).