Did you ever get that annoying problem that in your “Open With” menu the same app shows multiple times?

Fortunately, this is easy to fix. Just open up Terminal and paste in the following lines (all at once) to fix the problem!

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user && pkill Finder

Cause of the problem: When you delete an application, its entry in the “Open With” menu is not deleted. This also applies to app updates, where the old version of the app is deleted and replaced by a new one (which gets its own menu entry). The problem probably only occurs for non-Mac App Store apps.