The Open With menu lets you open documents with an application other than the one associated with the document type. For example, you might want to open a JPEG image with Photoshop instead of Apple's Preview. You can easily do this by right-clicking on the document (in our example, a JPEG image) and selecting Open With from the pop-up menu. This is my favorite way to quickly open documents in other applications. The Open With menu shows all the applications you have installed on your Mac that can work with the selected document.

One downside to the Open With menu is that it can become quite long over time as you install and remove applications on your Mac. It can also start to show duplicate applications. For example, my Open With menu shows four entries for Photoshop, even though I only have one version of Photoshop on my Mac. The Open With menu can become cluttered with duplicates every time you clone your startup drive or connect drives that contain copies of applications. Sometimes it just seems to happen because a dog barked at the full moon in the middle of the night.

Resetting the Open With menu removes duplicates and ghost applications (that you've deleted) from the list. You reset the Open With menu by rebuilding the Launch Services database that maintains your Mac. There are multiple ways to rebuild the Launch Services database, including third-party utilities like Cocktail and Onxy.

If you don't have a system utility that can rebuild the Launch Services database, don't worry. You can do it yourself via Terminal.