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 nine alternatives to KeyCue for a variety of platforms, including Mac, Windows, Linux, Web-based and Android apps. The best KeyCue alternative is KeyCombiner, which is free. Other great apps like KeyCue are Paletro, ShowMeYourHotKeys, KeyClu and CheatKeys.
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.