Jira - The #1 software development tool used by agile teams. Jira Software is built for every member of your software team to plan, track, and release great software.
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.
Redmine - Flexible project management web application
jtrac - JTrac is an open source and highly customizable issue-tracking web-application written in Java.
PlanShell - PlanShell offer a secure, low cost, unlimited project management & issue tracking redmine hosting services
Bugify - Bugify is a simple PHP issue tracker, designed to offer powerful bug tracking capabilities in an easy to use system.