LaunchBar, whose primary purpose isn't nearly as necessary since Spotlight mostly took up that functionality (can you tell I've been using it for a while?), but

LaunchBar, whose primary purpose isn't nearly as necessary since Spotlight mostly took up that functionality (can you tell I've been using it for a while?), but provides both very quick access to a simple calculator, and a pretty robust clipboard manager. HiDock, which automatically switches my Dock between left-edge (when I'm using my laptop on its own) and bottom-edge (when I have it docked with the much larger screen on my desk). iStatMenus, which makes it vastly easier to tell when my Bluetooth mice and keyboards need charging. Fluor, which automatically switches my function keys between their macOS "media/feature key" setting and standard function keys based on app (primarily so I can use them as intended in games like Final Fantasy XIV). MacPorts, IMO still the superior macOS package manager. I honestly don't know why Homebrew suddenly started getting so much attention several years ago, to the point that many devs don't even appear to know that there is another option, when MacPorts is older and doesn't take over an otherwise highly useful directory (/usr/local; MacPorts uses /opt/local).