New submitter omar.sahal writes "Bret Victor demoed the idea of instant feedback on your code. ... Allowing the programmer to instantly see what his program is doing. Chris Granger has turned this novel idea into Light Table — a new IDE designed to make use of Victor's insights."
The screenshots make this look like it could be genuinely useful — like a much fancier and more functional combination of features from SLIME and Speedbar. There's a Google group for those wanting to track development. There's no code yet, but source is promised: "I can guarantee you that Light Table will be built on top of the technologies that are freely available to us today. As such, I believe it only fair that the core of Light Table be open sourced once it is launched, while some of the plugins may remained closed source."