The best programs are the ones you install, forget about and use everyday. These programs integrate so well into the environment that they become part of your work flow. Katmouse is just such a program. Simply put, it allows you to scroll the window beneath the mouse cursor, even if the window does not have input focus. It’s a simple behavior that it is instantly useful and requires no memorization to use.
I wish there was more to say about it but that’s really it. It just works and perhaps that’s the best praise anyone can give a program. Highly recommended.