Mantis is a PHP/MySQL-based bugtracking system. It is extremely easy to deploy and customize, and features one of the simplest and cleanest interfaces of any tracking tool available. It supports multiple projects and email notification, and is localized for over 18 languages. Version 1.0.3 came with many bug fixes including : A bug in string_sanitize_url() was fixed. Numerous MS SQL bugs were fixed. The Global Profiles list is now sorted. is_writable() in install.php was fixed. A possible redirect to blank page for new admins was fixed. A wrong strpos function call was fixed. fixed_in_version was renamed to Fixed_in_version during database migration.
http://community.phpmagazine.net/upload/2006/05/mantis-thumb.png
In addition to bugtracking system, I’ve been using Mantis also for task and project management, and personally I find it excellent tool because lot of tasks for me are better managed as tasks. Demo of Mantis is available online, you can see changelog for changes, and download the latest release from sourceforge’s project page.