OS X Package Manager.
Package Assistant is a little tool to manage OS X packages. You can check their integrity (whether their files are correctly installed or not) or you can remove them.
When I first met OS X I was amazed by the way applications were installed and uninstalled (by drag-and-dropping), that's why I got a little disappointed when I found out that there were some files (.pkg and .mpkg) that couldn't be uninstalled from the system unless the vendor of each package provided an uninstaller. I decided to make my first OS X app to solve this issue.