iOS: If you've ever taken a hasty photo on your phone and didn't leave enough room on the outside, AntiCrop is the app can "uncrop" those photos by filling in the edges with just a few swipes.
You've probably heard about content-aware fills before, which remove blemishes from photos by using information from elsewhere in the picture. AntiCrop uses that same technique to "uncrop" your photo from the edges out, so you can get a bit more of that beautiful sunset in the photo, even if you didn't get it in the original shot. It also lets you straighten the photo without having to crop it down (see the image to the right for an example).
It won't work on every photo, of course. You'll want something with a relatively uniform background, like a clean landscape, for it to work well. The image at the right is one of AntiCrop's promotional images, but the top image is one I took on my phone, and it's a good example of what does and doesn't work. You can see that it does a pretty good job of filling in the beach and water areas, but the building on the left gets blurry because it's too complicated.
Also, since the image is dark, you can see blur lines where the image originally ended -- sometimes these show through, sometimes they don't, depending on the lightness and complexity of your photo. So, it isn't always perfect, but for the price, it's nice to be get the chance to tweak around your photos after the fact (without the effort or expense of something like Photoshop).
AntiCrop is a $0.99 download for iPhone and iPad.