Available from FreeMacSoft, the freeware (donations accepted) AppCleaner does what it says on the tin. Just like AppZapper, you can drag-and-drop the offending application onto AppCleaner to locate and delete all the associated files. Alternatively you can hit the Applications, Widgets or Others tabs to find and delete things directly from AppCleaner. "Others" thankfully includes Preference Panes, so you can get rid of any unwanted additions to your System Preferences with ease.
So far so good, it does exactly what AppZapper does, but it's free. AppCleaner does have one unique feature, however, and that's "SmartDelete." An option in the preferences, SmartDelete allows you to carry on deleting apps the way Apple intended by just sending them to the trash, but with the added benefit of trashing all the associated files automatically. While SmartDelete is running, AppCleaner is supposed to detect that you've trashed an app and offer to find the associated files for you. I couldn't get it to work, but free's free right?
If you want to get rid of some applications you've installed but never use, AppCleaner does the job fine. It may not be the most comprehensive Mac cleaning app out there, but as uninstallers go, AppCleaner is free and works great.Perhaps with Lion landing soon, now is the time to start clearing out the cobwebs and get your Mac ready for the shiny new OS X 10.7.
Thanks to brijazz for the suggestion.