StepMania

Okay, let's use the "unofficial" request form:

Program: StepMania

License: Open Source/GPL (I suppose; the website says that "The source code to StepMania is freely available" (check on http://www.stepmania.com/wiki/About_StepMania)

Description: A step-dance simulator, much like Dance Dance Revolution. Supports characters, videos, animated backgrounds and much more (as far as I'm concerned).

Website: http://www.stepmania.com/

Other: Version 3.9 (latest stable version) saves nothing in registry (except for the SMZip extension association).