Flat-pack softbox for my flash.
It makes a great difference on close-ups but obviously the diffusion reduces the effective range.
Inside the fabric is silvered, acting as a reflector, so flipping down the wide angle diffuser on the Canon 580EX will give a more even illumination of the front of the box.
You can see reflected in the kitten's eye that without that extra diffuser there is an appreciable hot spot, but the shadows are diffuse and it's a great easily portable lighting tool.