MantisBT is a free popular web-based bugtracking system. It is written in the PHP scripting language and works with MySQL, MS SQL, and PostgreSQL databases and a webserver. MantisBT can be installed on Windows, Linux, Mac OS, OS/2, and others. Almost any web browser should be able to function as a client.
Simple User Experience
Supports any platform that runs PHP (Windows, Linux, Mac, Solaris, AS400/i5, etc)
Available in 68 localizations.
Simple/Advanced Issue Pages
Multiple Projects per instance
Support for Projects, Sub-Projects, and Categories.
Users can have a different access level per project
My View Page
Search and Filter
Full Text Search
Shared Filters (across users / projects)
Built-in Reporting (reports / graphs)
Users can monitor specific issues
Attachments (can be saved on webserver or in database - can also backup to an FTP account)
Issue Change History
RSS Feeds (news, issues matching saved filters, issues matching a specific project)
Customizable issue workflow
Sponsorships Support - users are able to place bounties or sponsorships for specific issues, also developers can track such sponsorships / payments.
Signup with Captcha and Email Confirmation.
Self-Service Reset Password Support
Export to csv, Microsoft Excel, Microsoft Word
And Much More
by a Guest - A.M. - February 20, 2015, 7:34 pm
The documentation is easy to understand, it's an efficient tool for tracking bugs and also for software versioning. It's easy to extend it according to your needs, there are some great (free) plugins like agileMantis you can use if you want more advanced bug management.