Developer website: StimpSoft, Inc.
Smell-O-Mints is a Periodic table of the elements for the Mac. It's not as full-featured as a lot of other Periodic tables out there, but it's free and looks very nice. Especially if you put it next to the coffee table by the ferns.
Version 2.32: Bug fix: progress window now properly closes when finished loading.
Mac OS X 10.4 or later