Walker System is a character walk animation addon for Blender, it's primary made to work with Rigify, but can be used on other rig systems.
In computer animation walk animation is usually done using walk cycle. It's fast to make animation of character walking using this method, and it's easy to set complex motions because we're dealing with short loops. Downside of this method is foot sliding on the floor, which can be easily fixed if character is walking at constant rate, on straight path and flat ground.
Walker System expends walk cycle method with a solution that provides full control over feet and snapping of feet to the ground so it works fine on all paths or ground shapes.
It doesn't make a walk cycle, just fix problems with foot sliding when using a walk cycle on curved path and leveled ground.