Agilo for Scrum is a simple, web-based and straightforward tool to support the Scrum process. Agilo is based on Trac a very successful and widespread Ticket Tracking System, and developed using the Python
Bringing you a powerful Bug tracking solution and a top notch community to go along with it. Search for bugs, get solutions, consult. Enjoy the power of a community tightened by bugs.
Mantis 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. Mantis has been installed on Windows, Linux, Mac OS, OS/2, and others