Free software for bug tracking and project management

Mantis Bug Tracker is a web-based system designed primarily for tracking bugs and finding defects in software. However, it can also be used for tracking more general issues and even as a project management tool. It is ideal for companies that either create their own software or need to keep track of software issues. Mantis Bug Tracker allows a large number of different users to interact and track issues among multiple projects, and is usable on any of the main operating systems.