Codegiant includes pretty yet powerful tools for agile project management. It is meant to be a single platform for project management. People are loving it as a great alternative to Jira as it is faster with better UI/UX and is free to use for upto 5 users.
Codegiant includes issue tracking, hosted Git repositories, continuous integration and documentation in a single platform. Slack Integrations, API integrations are also in place with Codegiant.
Mantis Bug Tracker - Mantis Bug Tracker is a free and open source, web-based bug tracking system.
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.
Pivotal Tracker - Pivotal Tracker: The awesome, lightweight, agile project management tool for software teams. Get your 30-day Free Trial started today!
Redmine - Flexible project management web application
openDesktop.org - The website openDesktop.
Bugzilla - Bugzilla is a "Defect Tracking System" or "Bug-Tracking System".