Wreak Havoc With Photos
LiveQuartz is a CoreImage editor; that is, it's an interface by which you can access the CoreImage components that reside within the OSX operating system -- specifically OS 10.4.
When an image is dropped onto the interface you can tweak the image by applying various filters. Each filter is applied as a new layer over the image, so you can then toggle the applied filters to fine-tune the effect.
As images editors go, it's a little bit unusual in the method by which you perform the various actions, and a little bit buggy. However, I find it the easiest to use when I just want to "mess around" with an image.