Redmine is a flexible project management web application. Written using the Ruby on Rails framework, it is cross-platform and cross-database.
Redmine is open source and released under the terms of the GNU General Public License v2 (GPL).
Some of the main features of Redmine are:
Multiple projects support
Flexible role based access control
Flexible issue tracking system
Gantt chart and calendar
News, documents & files management
Feeds & email notifications
Per project wiki
Per project forums
Custom fields for issues, time-entries, projects and users
SCM integration (SVN, CVS, Git, Mercurial, Bazaar and Darcs)