This was a system I designed and implemented for an exhibit at the (now defunct) Boston Computer Museum. It was an interesting challenge – can you build something that conveys something about programming but is usable and learnable by tourists with short attention spans?
This was done at the Media Lab and predated Scratch. I don't have a patent on programming with blocks but still feel I deserved a bit more credit for developing the ideas.
The block-programming designs started here also made their way into the BioBike VPL, Enflame, and Vaguely. The source is on Github but it depends on a version of Mac Common Lisp and the Mac OS that has been obsolete for decades.