Simple and handy overview of all shortcuts for any application. Easy to use: just press ⌘ twice and hold to see the list.
KeyClu's answer
The CheatSheet becomes not available, so here its successor.
KeyCue - Menu shortcuts are supposed to provide quick access to frequently used menu commands.
Keysmith - Create custom keyboard shortcuts for your Mac and the web
CheatKeys - View Windows keyboard shortcuts in the current application.
Shortcut Keeper - Shortcut Keeper is a simple macOS app that lets you store the keyboard shortcuts you use daily in your apps.Save all the shortcuts you want to learn and remember.Keep it on the side while using your apps and quickly check your saved shortcuts!
cheat - Cheat allows you to create and view interactive cheatsheets on the command-line.
ShowMeYourHotKeys - Show All shorcuts of applications!