Just came across Pxlr the other day – working on a machine without Photoshop or The Gimp – and thought I was done for!
But no!
This online tool came to my rescue – and very useful it is too: supporting layers, opacity, scaling including a full range of selection and cut and crop etc.
Apparently it’s also available on mobile platforms like iPhone and Android – though I haven’t tested these yet! Why not nip over to the good folks at Pixlr and take a look?