Payment systems while working at a pizza place
I'll chime in with a lesson learned from my own experience in niche POS systems: it can be amazingly valuable (in certain contexts) to let clerks pause sales and put them off to one side (think "git stash", but for sales). Customers wander in and out, run back for one more thing, or put things on hold while they go out to get cash out of an ATM. Letting a clerk wrap up a whole sale with context (some items rung up, payments created but not processed, etc.) and put it on a shelf to restore later is a superpower for POS systems.<p>And that's not even _starting_ on the nonsense and bizarre home-rolled systems that small businesses concoct around layaways.