One very deep notion in there is "identity within the system". Some people learned it from Smalltalk; I learned it from LambdaMOO. I respectfully submit that p

One very deep notion in there is "identity within the system". Some people learned it from Smalltalk; I learned it from LambdaMOO. I respectfully submit that people who are focusing overmuch attention on Light Table "because Bret Victor" are mostly missing the point. As Bret points out, there's a lot you can learn about these things from existing (even old) systems. If you already know Smalltalk, Logo, HyperCard and Rocky's Boots (I'd missed out on this one but it reminds me of Robot Odyssey which I did play), you could do worse than go and play with LambdaMOO for a little while. (ETA: it turns out that Roboy Odyssey was a sequel to Rocky's Boots.)