Have you looked at Specify? <http://specifysoftware.org/> I was actually exploring it a bit yesterday, seeing if I could possibly adapt it to manage an archaeological repository collection. I liked it because it: could be used on Mac or PC, is open source & semi-local (to Missouri), has been around since the late 80’s, and “Collaborating institutions can use Specify for no charge.” However, I have never actually used it before, so I don’t know if it’s as awesome as it sounds.
Good luck!
