When I right click on a file on my mac, I started seeing multiple apps being listed in the “Open with…” menu.

Typically this list of apps are the apps which can open the file. Seeing the same application listed multiple times in the “Open With…” list doesn’t harm anything but is definitely annoying!

So I googled the problem, and saw others were having the same issue. Basically the launchServices database gets corrupted which leads to this problem.

To fix on Mountain Lion:

1. Open Terminal.app in the /Applications/Utilities/ folder.
2. run

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

3. Restart

If you don’t like using the command line, the free tool Onyx also has an option under Maintenance -> Rebuild -> launchservices.

Another option is to uninstall the application which is showing up multiple time and install it back.

All the above options work.