Mantis is #8 in Top 18 Issue Trackers
MantisBT is a free popular web-based bugtracking system (feature list). It is written in the PHP scripting language and works with MySQL, MS SQL, and PostgreSQL databases and a webserver. MantisBT has been installed on Windows, Linux, Mac OS, OS/2, and others. Almost any web browser should be able to function as a client. It is released under the terms of the GNU General Public License (GPL).
Positions in ratings
#8 in Top 18 Issue Trackers
The best alternatives to Mantis are: JIRA, Bugzilla, Redmine, Trac, Trello