TrashMe is a system maintenance tool for Mac OS X computers. It allows you to delete your files and applications in a very clean way. Unlike Finder, when TrashMe deletes an App, it generally looks for related files that are installed somewhere else rather than in the Applications folder. Thus, applications uninstalled using this tool won't leave configuration files around that can later cause problems.
The application can be used in a few different ways. For example, when you first launch it, you will see a drop zone, where you can drag and drop .app files to tell the app that you want to uninstall them. Once you drop the files, a quick search will be carried out to find relevant, related files. Or, you can simply click on the "Applications" button, which will bring up a list of all the Apps in your Applications folder. This is the method that I generally use the most, since I get to see very quickly all the apps that are installed and that I don't need. Once you have selected the apps that you want to delete and related files have been found, you can go ahead and delete it.
In my testing, the app did a great job of finding lots of files installed on other parts of my Mac. For example, I often saw it find Growl and list files that I had no idea about.