This document discusses Redmine, an open source project management and issue tracking tool built using Ruby on Rails. It provides information on what Redmine is, how to install and use it, and how to build plugins for it. Key features of Redmine include multiple project support, flexible access control and issue tracking, a Gantt chart and calendar, and document management. Building plugins for Redmine requires Ruby to be installed, and the document provides references on the plugin tutorial and other Redmine resources.