Ranked in these QuestionsQuestion Ranking
Pro Free and open-source
Redmine is a free and open source tool.
Pro Visually appealing and has high usability
Redmine's UI is very simple and easy to learn to use. It does not overwhelm users with many options and information at once.
Pro Built In Wiki
Pro Built in Integration for GIT, SVN, & CVS
Pro Plugins support
If there is additional features set you want you can find or write plugins to extend the ability.