OnyX: Make OS X Spill the Beans
Leatherman as Metaphor
Most guys know what a Leatherman tool is; it's a multifunction gizmo that arranges most of the tools you routinely need into a foldable item that can be carried on your belt or in your pocket. It's physically big enough to do most jobs, but not so big that you can't have it available to you all the time. Now in the interest of full disclosure, I should admit that I carry the smaller "Micra" version of the Leatherman tool with me everywhere I go. It's proven to be just so doggone useful, I want it around and always within reach.
That's sort of what I think about OnyX. It's a freeware program from Titanium Software that is really an interface to the Unix underpinnings of Mac OS X. You can access the tools that Unix provides and use them to get to a deeper understanding of what your computer is doing, which is especially helpful if you are trying to troubleshoot a problem. Like a Leatherman tool, OnyX pries open the maintenance side of OS X and helps you screw around with it.