Mac OS: There are plenty of uninstallers for Mac, but TrashMe is smart enough to seek out preference files and remove them when you remove an app, and can also uninstall applications you don't have write access to.
Uninstalling apps on the Mac is usually as simple as dragging an app to the trash, but many applications leave .plist files and other preference files littered around your system that will take up space when the app is gone. Like AppCleaner and AppTrap, TrashMe identifies those files and trashes them along with the application in question.
What makes TrashMe special is that with the help of an add-on fron the developers, the app will also change permissions on apps you may not have write access to and uninstall them, which is perfect if you inherited a Mac from a friend or family member. TrashMe is $7.49 in the Mac App Store.