This document provides an overview and outline of open source software options for libraries. It begins by clarifying the difference between open source software and freeware, noting that open source software licenses are open and customizable. It then lists several benefits of open source software such as reduced costs, increased flexibility, and improved security compared to proprietary options. While open source code can be modified, the document acknowledges that many libraries lack the time or resources to make changes. However, open source ensures that development will continue even if a specific organization stops supporting a project. The document provides numerous examples of open source software that libraries can use and concludes with a checklist for evaluating different open source products.