CheatSheet is a great little Mac OSX app if you’re a fan of keyboard shortcuts. Once set up, all you need to do is hold down the command (cmd or ⌘) key for a couple of seconds and CheatSheet will display the available keyboard shortcuts available within your current application.
It’s a free app, but since it works outside of Apple’s “walled garden” you can’t get it in the app store. You just need to go to the Cheatsheet site and download the zip file, extract the file, and run the app. You’ll see a security notification that you’ll need to whitelist that app in your Privacy>Accessibility settings–this is what gives the app the capability of reading your keystroke to know you’re holding down the ⌘ key.
Incidentally, automatically restricting apps that don’t come from the App Store is also one of the reasons you don’t see nearly as much malware on Macs.
It’s a nice, free, and pretty easy-to-install utility. Check it out if you’re so inclined.