The fact is that the foundational software in place in nearly every industry is being built with open source components. Where software applications are still proprietary or closed, those systems are themselves often built upon open source applications like open source web services, database management systems, programming languages, and operating systems. It’s the same story in the library world. Library software providers offering the latest and greatest software solution for many thousands of dollars a year are building these solutions with open source software. However, full-fledged open source applications built with the same underlying technologies are available to libraries at no cost for the software itself. Each of these applications have their own unique and interesting history and communities supporting them. For the reader unfamiliar with open source software or apprehensive about using these applications in their library, this guide: