I was inspired by the excellent set of mathematical gif animations at http://mathworld.wolfram.com/topics/AnimatedGIFs.html and then re-visited Virtual Manipulatives at http://nlvm.usu.edu/en/nav/vlibrary.html and http://www.fi.uu.nl/wisweb/en/welcome.html
Seems that there is a continuum:
Objects for viewing
Objects for manipulating & viewing
Objects for re-programming, manipulating and viewing
Maybe if the third option was done by somebody more skilled than me, it would be the most powerful learning object. There's your challenge!