KeyCue is described as 'Menu shortcuts are supposed to provide quick access to frequently used menu commands. But honestly: how many menu shortcuts do you know by heart? KeyCue helps you to use your Mac OS X applications more effectively by displaying a concise table of all currently available menu' and is a Cheat Sheet in the os & utilities category. There are more than 10 alternatives to KeyCue for a variety of platforms, including Mac, Windows, Linux, Web-based and Android apps. The best KeyCue alternative is KeyMinder, which is both free and Open Source. Other great apps like KeyCue are KeyCombiner, Paletro, ShowMeYourHotKeys and KeyClu.
Paletro is just as nice/powerful as KeyCue IMO at less than half the price. It's also included in Setapp if you subscribe to that.