Photoshop is perhaps Adobe's best-known and most widely used program. It is a photo editing application but in reality it's capacity far exceeds editing. In Photoshop, as well as making color, filter and cropping edits, its possible to stitch multiple images on top of one another, remove textures and other features of the photo and work with a wide array of filters. Its a versatile photo editing and organizing system.
There are many websites and videos devoted to Photoshop. Here is a sample: