Back in 2001, when I was 18, I made rendered 3D animations in my spare time with the freeware raytracer POV-Ray. POV-Ray doesn't have a graphical front-end like 3Ds Max etc; instead you make your images and animations with a scripting language.
Among many other things, I made a walking system for POV-Ray. Here are some of the things it could do:
Making the system was a rather big challenge. POV-Ray has no support for keyframe animation so I had to make all animation 100% procedural and animate it by scripting! This was a very slow process and I never got as far with the system as I had in mind.
Now, using the Unity game engine, I am creating a walking system again. This one is different. In the system for POV-Ray (that was made for offline rendering) every step was calculated in advance. With the new system, characters need to respond dynamically from input from the player or from AI. Also, this time I have keyframe animation, skeletal animation, animation blending, and many other features at my disposal, which makes it easier to do more advanced things, but which also bring new challenges.
Although the new walking system for Unity will be very different from the old walking system for POV-Ray, I still think the video here will help make it easier to grasp what the system will be all about.