Physics Model Editors
Physics Model Editor - The first of the two. Comes with extensive docs, and the author will also help you out if you e-mail him.
PME was found at: AMUG, America Online
Playsets - Originated on E-world. Although easier to use than Physics Model Editor, there are less values you can control. Playsets reminds me of those Face-tracing books where you can take different heads and draw them with different ears, eyes, mouths, etc.
MPE was found at: AMUG, America Online, E-world