Photoshop Touch is now available for Android phones and iPhone/iPod Touch devices, after originally being released for tablets last year. Photoshop Touch is much more advanced than the free Photoshop Express, with features like layers, selection tools, adjustments and filters.
The Scribble Select lets you use your finger to select, save or discard parts of your images. Photoshop Touch also has edge-aware painting, to increase the accuracy of your finger on the touchscreen, tone and color adjustment and a set of interactive tutorials.
On top of this you work with Photoshop compatible formats, and can upload to Adobe Creative Cloud, so you can work on them further on the desktop version.
