In the Finder when you are looking at a file, you can right-click on the file and select the "Open With" menu option to open the selected file with an application of your choice. Over time, this menu of options can become overly bloated with old applications that you have either uninstalled or which you no longer use. If you want, you can clear out the options shown when selection "Open With". If you do this, the list will rebuild itself and all of the clutter will be removed... until it builds back up again :)

To reset the "Open With" menu, open the Finder and navigate to the Home / Library / Preferences folder, where Home is your home directory (usually named the same as your user name). Once there, locate the file named com.apple.LaunchServices.plist and delete that file. Next time you right-click and choose "Open With", it will rebuild the list and any programs that have since been removed will no longer be shown.