Bugify - Bugify is a simple PHP issue tracker, designed to offer powerful bug tracking capabilities in an easy to use system.
Flyspray - The bug killer!
16bugs - 16bugs is an all-in-one bug tracking software that makes it easier for you to manage all sorts of bugs in performance with the simple interface; ultimately, you will be more productive for sure.
Collabtive - Collabtive is a web-based project management software.
Traq - Traq is a PHP powered project manager and issue tracker featuring multiple projects, milestones...
Teamwork - The Project Management App for Professionals. The most powerful and simple way to collaborate with your team.