cheat allows you to create and view interactive cheatsheets on the command-line. It was designed to help remind *nix system administrators of options for commands that they use frequently, but not frequently enough to remember.
Megapedia by the BBC GEL is designed to be a table of universal shortcuts. It is envisaged as a one-stop shop for anyone using or creating keyboard shortcuts for either Windows or Mac. It is also intended to be something of a shortcuts library for the end user, of a variety of typical functions and features.