Quick Resizer - My first Mac App
I've created a few iOS and Android apps for mobile devices and tablets, but just a few days ago, my first 'desktop' app (for Mac OS X 10.7+) was released on the Mac App Store.
Behold, Quick Resizer ($0.99 on the Mac App Store):
I created the app mostly because I realized I would often drag an image to Photoshop to simply resize it from something like 1024x768 to 500 pixels wide, constrained. Quick Resizer makes resizing JPEGs and PNG files super-easy, and everything can be done from the keyboard (or the mouse, if you're so inclined).
Developing for the Mac is a bit different than the iPhone, but Objective-C and the libraries included are very similar, so it wasn't like creating the first iOS app!