Windows/Mac: Freeware application ImageSorter organizes images by color, date taken, name, or size. According to ImageSorter's developer, the main purpose of the application is to help you find pictures you've taken when you remember how the picture looks (by color) but have no idea where it is on your computer. The application is pretty simple to get the hang of, and it does offer an interesting way to browse and sort images, and while it's not going to replace image management apps like Picasa or iPhoto, it's a great tool for finding that lost photo under the right circumstances. For a better look at how it works, check out the video demo from the developer (in German).
ImageSorter [via gHacks]