What are the nicest apps you use day to day?

By “nicest” I mean polished and pleasant to use: good defaults, discoverable UI, responsive/performance-conscious, and visually calm.

Recently I tried LocalSend and it immediately felt modern and well-designed (even the website). I don’t use it often because Syncthing covers most of my file-sharing, but it stood out enough that I actively wanted to use it more.