This presentation from Bret Victor is by far the best conference talk I've heard in a long time. Bret invents tools that enable people to understand and create. He has designed experimental UI concepts at Apple, interactive data graphics for Al Gore's book (Our Choice), and musical instruments at Alesis. Bret's talk is on principles, but for many developers what’s really awesome are the software development tools he demos.

This talk was given at the Canadian University Software Engineering Conference CUSEC 2012. For more on Bret, see worrydream.com.