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