ProofHQ is a collaborative tool for reviewing creative projects such as photography and graphic design. The tool allows you to upload anything from a PDFs, PSDs, and JPGs to Word and PowerPoint files up to 75 MB. The functionality is a bit like a mashup of Flickr and Skitch. It allows users to annotate, mark up, and comment on the work. The art can be embedded into a web site with the provided embed code.