Windows only: The browser wars are in full swing, and many of us are running multiple browsers on our computers for various tasks. Browser Chooser makes it easier for you to direct new links into your preferred browser each time.
After you download Browser Chooser, just run it (no need to install—it's a portable application), hit the Options button, and point it toward the browsers you use regularly. Then hit the Miscellaneous tab and set Browser Chooser as your default browser. It's not a browser, of course—this is just a workaround so that Browser Chooser will launch whenever any other application tries launching a link. When it does, you click on the browser you want to open said link in, and Browser Chooser takes care of the rest.
Honestly, if you don't use more than one browser except on very rare occasions, Browser Chooser is probably more tedious than it's worth; personally, I kind of like the idea. Browser Chooser is a free, open-source application for Windows only.