PNGGauntlet isn't being updated anymore. It still works fine but you might want to look at the alternatives listed below!
PNGGauntlet Screenshot


The software license for PNGGauntlet permits unlimited distribution as long as nobody charges money for it, modifies it, or packages it with other software without my permission. It also frees me from any liability from your use of the software. A copy of the actual license is included in the installation and is viewable from the "About" dialog.