Here’s one for those who use Apple’s Notes app for storing bits of information. By default, Notes in macOS gives you a single window, with each note listed in a sidebar. But what if you want to see two notes at once? Or keep one always available no matter what else you’re doing? Click the desired note in the sidebar, and then choose Window > Float Selected Notes to open them in their own windows. Or, just double-click the note in the sidebar, then choose Window > Float on Top. It’s still a normal window that you can move and resize and close, but no other app will appear over it. See how Safari is the frontmost app below, but the Notes window is on top?