If anyone can help figure out how to trigger the leap keys in the emulator, I'm all ears:

https://archive.org/details/canoncat

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It's fascinating to compare a tool like this to the direction the Macintosh actually took — though Jef Raskin conceived the project in the early days of Apple, the graphical user interface took its design cues from the research at Xerox Parc instead. The Humane Interface is Raskin's book on the principles behind a product like this: focus on spatial context with a zooming UI, be forgiving with ubiquitous undo, provide one way of doing things, never trap the user in a mode. A lot of those ideas are embedded in the interfaces we have today, but they feel entirely orthogonal to the discoverability that a Parc-style GUI provides.