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=eEz08IlcNMgGit repositories have the lovely properties that deletes aren't propagated. Shared/cloud storage sync deletes across devices.
Accidentally deleting content in a local git repo, and even pushing it, is a safe operation.
Lovely example of using fuel to debug compiler optimisation passes in GHC: