Steve Jobs famously asked for smooth scrolling (i.e. not line-by-line) in a Smalltalk demonstration and they changed the UI live.
Here's a lovely 2 minute YouTube video demonstrating that modification: https://www.youtube.com/watch?v=eEz08IlcNMg
miniblog.
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Git 2.17 has some really nice diff tweaks: colouring lines that have moved without modification, and even showing context by function rather than just N lines!
If you wanted to write a program that would still work (without modification) in 20 years, what language/platform would you use, and why?