Bill Powers maintained a personal site, connected to his email account, at
http://www.frontier.net/~powers_w/ Now closed.
Repaired and mirrored in September 2015 before Bill's account closed.
Bill Powers' Personal Site Mirrored Here.
Where Bill's links to files were broken, I have linked to the same or better-performing versions. Fortunately, I downloaded demo files from Bill's site in 2003 and 2004. Demos I did not download were apparently added later. Links to these worked, so this site is now complete the way Bill left it.
Note that some of Bill's demos are unique to this personal site:
Arm with Artificial Cerebellum
Stopping a car
Demos at http://www.livingcontrolsystems.com/demos/tutor_pct.html are likely to be the latest and most functional versions, with the most complete documentation. (I tested all available versions and reviewed, formatted documentation in consultation with Bill when in 2006 I set up demos at the livingcontrolsystems site).