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.
Pretzel - Keyboard shortcuts for the app you're currently using
KeyCue - Menu shortcuts are supposed to provide quick access to frequently used menu commands.
Stacky - Simple app enhancing windows task bar functionality with stacks of shortcuts.
CheatKeys - View Windows keyboard shortcuts in the current application.
Runner Pro - Perform Sketch actions quicker with your keyboard
cheat - Cheat allows you to create and view interactive cheatsheets on the command-line.