cheat - Cheat allows you to create and view interactive cheatsheets on the command-line.
cheat.sh - The only cheat sheet you need Unified access to the best community driven documentation
explainshell - Match command-line arguments to their help.
CheatKeys - View Windows keyboard shortcuts in the current application.
KeyCue - Menu shortcuts are supposed to provide quick access to frequently used menu commands.
bropages - bro pages are concise examples of using command line programs