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.
Linear - Streamlined issue tracking for software teams
Redmine - Flexible project management web application
Distiller - Distiller's hosted continuous integration platform takes the pain out of mobile development through automated build, test, and deployment of your iOS apps.
Mantis Bug Tracker - Mantis Bug Tracker is a free and open source, web-based bug tracking system.
BugHerd - BugHerd: The Website Feedback Tool for Agencies