Mac: PopClip is a handy little Mac utility that allows you to add all kinds of options to a left-click menu and includes a way to make your own. PopMaker is an app that makes that process of making your own a lot easier.
PopMaker provides an easy-to-use interface for PopClip's extension maker. This way, you don't need to deal with the technical aspects of making your own extensions, and you can just get your idea out there and finished. Just load up the app, select the extension type, enter your settings, and you're all done. It's fast and easy to use, which makes PopClip a lot more fun to play around with. You can find the full guide on how to use it over on the PopMaker site.
PopMaker (free) [Brett Terpstra]