Menu bar tools live in the top-right strip of the screen and each do one job: show system stats, control external display brightness, run scripts, or hide clutter. On MacBooks with a notch, menu bar space is limited, which is why icon hiders like Ice, Hidden and Dozer are so widely used.
Most apps here are small, free and open source. Because they run all day, prefer native apps with low memory use, launch-at-login support and updates for the current macOS. MonitorControl adjusts external monitor brightness and volume, xbar and SwiftBar turn any shell script into a menu bar item, and SketchyBar replaces the bar with a fully scriptable one.