This is a concept which is not new (the apparently famous Berkley Tool Library” has been around since 1979) but the idea seems to be catching on in the United States and could have potential as a microfranchise. There was a recent post on Treehugger, which has been posted by EcoRealty. Kevin Kelly over at Cool Tools also spotted it a few years ago. There is also a Wikipedia entry which seems to have collected a list of operating tool libraries.
The concept could work beautifully in poorer communities given the right structure. My first thought is to combine it with a microcredit service. (I perhaps appeal to the 'combine it with microcredit' thought too often but the structure and scale of microcredit just begs for piggyback ventures.) When we traditionally think of libraries in the West we think of library cards, getting notices in the mail, etc., which would be obvious barrieres at the bottom of the pyramid. The microcredit innovation of group collateral could serve as the check on accountability and the established record keeping of microcredit institutions would be a great resource. Some microcredit groups I visited in Ghana already had a system of collective purchasing with group savings. Elect one of the women to be the tool librarian that way the MFI staff aren't burdened. The group can grow their library of tools collectively and rent them out to the community and then use the proceeds to buy mosquito nets, bam, and it comes back to my field of public health. See dad, I'm using my degree.
I can picture a tool library in Ghana having the FullBelly Peanut Grinder or KickStart's Brick Press, just to provide two quick examples. The idea of a tool library might also be appealing to financial donors who like to see their contribution touch multiple lives on a recurring basis. It's got potential.