Interactive editor based on the 'Inventing on Principle' talk
If you have not watched the talk (<a href="http://vimeo.com/36579366" rel="nofollow">http://vimeo.com/36579366</a>), I highly, 
highly recommend it. It's a very worthwhile and inspiring hour. In it 
Bret Victor (<a href="http://worrydream.com" rel="nofollow">http://worrydream.com</a>) discusses living life according to an
overriding principle. For him, that principle is that creative tools
should offer immediate feedback. He demonstrated a number of software
tools to that effect: creating computer art, games, algorithms,
electrical circuits and animations by seeing the effects in real-time
as you code them. The link is an implementation of one of his demos.<p>But more important than his particular example is the general theme.
Having a principle, which is a specific, actionable thing wrong with
the world (other examples from the talk: Larry Tesler and modal computing,
Richard Stallman and non-free software) is what allows you to have the
biggest impact. It's being able to look at something in the world and ask
yourself: does this match my principle, and if not, how can I fix it?