CheatSheet is lets you view available keyboard shortcuts in your current application. Just hold the ⌘-Key a bit longer to get a list of all active short cuts of the current application. It's as simple as that.
Alfred is an award-winning app for Mac OS X which boosts your efficiency with hotkeys, keywords, text expansion and more. Search your Mac and the web, and be more productive with custom actions to control your Mac.
Shortcuts.design is a small website that lists every shortcut a designer ever wants to know, all designapps in one place and in a simple and clear way. It's very usefull for beginning designers to quickly charge their workflow, when you switched to a new designtool or when you just want a reference for repeating actions!
Pretzel is Mac desktop app that shows and find keyboard shortcuts based on your current app.