As shown here: http://www.nathancoppedge.com/CatSpur_Shoes.html
This same design was submitted to Harvard's Big Idea Group around 2007-2009.
A type of shoe can be used with a springed extension on the heel, upon which is attached a roller ball. The result is enhanced walking ability. The spur or "catspur" on the heel would fold under the shoe for convenience when the catspur is not being used, so that the roller ball folds in front of the toe.
However, there is a problem with walking upon stairs, where the "cat spur" may drag upon a previous stair and cause tripping. Maybe an electronic countermeasure could be used to d-activate the spring when stairs are encountered.
A high-technology shoe potentially.
Reward: I'd like to wear some of these shoes sometime.