KeyCastr lets you share your keystrokes when creating screencasts, presenting, or collaborating with others. You can choose to display all keystrokes or command keys only, and there is also an option to include mouse clicks.
Stats is a free, open-source native menubar macOS application that displays your system stats in real-time.
Rectangle is a rewrite of Spectacle, a popular MacOS app used for managing and controlling windows via keyboard shortcuts. While mostly the same as Spectacle, Rectangle includes some extra features like the ability to snap windows to screen edges. Both apps are free and open source.
Reverses the direction of macOS scrolling, with independent settings for trackpads and mice.