Although Linux lives in lots of places, quite often it doesn't live alone. One case in point is Four Seasons Heating and Air Conditioning, where Mark Rasmussen oversees a mix of office productivity, VOIP, mobile dispatch, network security, and other applications running on a combination of Ubuntu Linux, Microsoft Windows, VMWare, BSD Unix, BlackBerry, and IBM AS/400.

Libraries--the brick-and-mortar institutions that amass book and periodical collections, not software modules, that is--get taken for granted in the Internet age.