iMage, for Mac OS X only, is a small, simple application whose goal is to do exactly one thing well: translate image files from one format to another. You shouldn’t need a manual or know a lot about image file formats to figure out how to use iMage. iMage knows about JPEG, GIF, PICT, TIFF, PDF (under Mac OS X) and several other formats. iMage can’t yet export GIF or PDF.
iMage is freeware. More information and download link here.