A friendly image editor that requires no internet connection or preexisting expertise. Just open a photo and have at it.
The app allows you to adjust attributes like brightness or contrast as well as add effects like a vignette or a border. It also allows you to flip, rotate and crop the image to your heart's desire. If you're a pro, you can even preview your edits on a histogram.
When you're done, just export the photo as a JPEG or a PNG with the quality settings of your choosing. You also get a choice in whether or not to keep metadata such as location information.