Jira is a commercial product with some dispensements on usage freely in certain contexts.

Features

• Manage bugs, features, tasks, improvements or any issue
• A clean and powerful user interface that is easy to understand for both business and technical users
• Map your business processes to custom workflows
• Track attachments, changes, components and versions
• Full text searching and powerful filtering (customisable, saveable, shareable and subscribeable!)
• Customisable dashboards and real-time statistics
• Enterprise permissioning and security
• Easily extended to and integrated with other systems (including email, RSS, Excel, XML and source control)
• Highly configurable notification options
• Runs on almost any hardware, OS and database platform
• Web service enabled for programmatic control (SOAP, XML-RPC and REST interfaces)