Bugzilla

•    Perl

Bugzilla is most popular and widely used "Defect Tracking System" or "Bug-Tracking System".

The Bug Genie - Issue Tracking and Project Management

•    PHP

The Bug Genie offers powerful Project Management, Wiki, Scrum support, LDAP authentication, Email notifications, and a huge list of features like timeline, roadmaps, attachments, SCM integration, time estimation, customized workflows and lot more.

MantisBT - Bug Tracking System in PHP

•    PHP

MantisBT is a web-based bug tracking system written in the PHP and works with MySQL, MS SQL, and PostgreSQL databases and a webserver. It supports multiple projects in a single instance. Its features set include Full text search, Built in Reports, Custom fields, Change History, RSS Feeds, Export to csv, Excel, Word, Upload attachments, Wiki Integration ,LDAP Integration, SOAP interface, Support for mobile devices, localization support and lot more.

Request Tracker - issue tracking system in CGI and Perl

•    Perl

Request Tracker is an enterprise-grade issue tracking system which thousands of organizations use for bug tracking, help desk ticketing, customer service, workflow processes, change management etc. This product is very stable and been around for over 10 years.

Trouble ticket express - Help desk software in Perl and CGI

•    Perl

It does everything from bug tracking and customer support to project management and to-do lists. It is light weight and web based as it is written in CGI. It has support for Ticket monitoring, Custom fields, Inventory Tracking, Custom fields, Email alerts, File attachments etc.

Eventum - issue tracking system

•    PHP

Eventum is a user-friendly and flexible issue tracking system that can be used by a support department to track incoming technical support requests, or by a software development team to quickly organize tasks and bugs.

Mantisbt - Bug Tracker

•    PHP

MantisBT is an open source issue tracker that provides a delicate balance between simplicity and power. Users are able to get started in minutes and start managing their projects while collaborating with their teammates and clients effectively.

Flyspray - Web-based Bug Tracking System in PHP

•    PHP

Flyspray is a lightweight, web-based bug tracking system written in PHP for assisting with software development and project managements. It supports Multiple projects, File attachments, Advanced search features, Atom/RSS feeds, Voting for tasks, Comments, Roadmaps and lot more.

SingleBugs - A simple single person bug tracker

•    Go

Singlebugs is a sole developer focused bug tracking tool. It takes its interface interface cues from Outlook's three panel design where the leftmost are the projects, the middle the issues and the right running commentary. It has a fulltext search bar which searches across all three streams making a very fluid development experience. Since it is designed to work locally it is also very fast.

Squash - Bug Smashing Tool

•    Ruby

Squash is an exception reporting and bug analysis tool from Square. Squash lets you analyze information about a bug to determine its root cause. Squash includes a full-featured commenting system, ticket-management system. Squash analyzes the stack trace of every exception, and determines which line in the backtrace is the source of the bug. It then uses git to figure out who might have caused the bug,

Community Add-on's for Gemini Issue Tracker

Countersoft Gemini Community Add-on's project providing users with additional integrations with Gemini, an ASP.NET Issue Tracker / Bug Tracker / Project Management platform.

Elastik - issue tracker that can track anything

•    PHP

The open source ticket/issue tracker that can track anything. It supports multiple projects and each project could have flexible fields, categories, status and status workflows. Data could be exported as CSV. Each User can customize their own dashboard.