Extension Changer is a small tool which I found to be similar to MAC OS X applications in many ways. And it does exactly what its name says: changes file extensions. I've been using computers since I was a child, but I was never able to understand the purpose of this kind of applications. My logic tells me that it’s easier to manually change the extension of a file than to install a tool that doesn't even work as expected.
The graphical interface of Extension Changer is identical with the one of most MAC applications. Also, like the vast majority of MAC tools, it comes with no real purpose. In order to change the extension of a file, you need to drag and drop that specific file in the interface of Extension Changer. Afterward, type-in the desired extension, and click on "Change". The extension will be changed and the program will be automatically closed. These are just too many steps for such a basic operation. Moreover, you have to run the program for every extension that you want to be changed. Quite annoying, I may say.
To end on a positive note, Extension Changer is an open-source tool and you are free to use it.