Bugzilla

•    Perl

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

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.

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.

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.

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,

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.

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.

JTrac

•    Java

JTrac is an open source and highly customizable issue-tracking web-application written in Java.

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.

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.

Bug.Net Defect Tracking Components

Bug.Net server-side controls and components to add defect (bug) tracking to your current ASP.NET website.

Bosco Bug Tracking System

•    PHP

Bosco is a rewrite of the popular Bugzilla defect tracking software in PHP. Among its goals are database-independence and ease of maintenance and modification. An API is also planned to allow external applications to work with Bosco's data.

sBugs Defect Tracking System

•    Java

sBugs is a defect tracking system written in Java, using JSP and PostgreSQL. It aims to be easy to install, maintain, and use. It does not have all the bells and whistles of a system like Bugzilla, but is feature-rich and extendable.

# Track - Bug tracking system

Sharp Track is web-based bug tracking system. It's developed in ASP.NET (C#, MVC).

Fossil

•    C

Fossil is a distributed version control like Git and Mercurial. Fossil also supports distributed bug tracking and distributed wiki all in a single integrated package. It is simple, high-reliability, distributed software configuration management.

QuickRadar - Mac app to simplify posting bug reports to Apple's Radar bug tracking system.

•    Objective-C

Mac app to simplify posting bug reports to Apple's Radar bug tracking system. It provides a global hotkey to open a window in which to enter a bug report, which can be easily submitted to Apple. The code is in just as bad a state. The web scraping is done in one big method which chains xpaths together to plot a course through the web site, and currently it spits out all the logs I was using while trying to get something that could post to Radar.

Trac - Integrated SCM and Project Management

•    Python

Trac is a lightweight project management tool that is implemented as a web-based application. It has an enhanced wiki and issue tracking system for software development projects. Trac will impose as little as possible on a team's established development process and policies.

trac - Trac is an enhanced wiki and issue tracking system for software development projects (mirror)

•    Python

Trac is a minimalistic web-based software project management and bug/issue tracking system. It provides an interface to the Git and Subversion revision control systems, an integrated wiki, flexible issue tracking and convenient report facilities. Trac is distributed using the modified BSD License.