RT is an industrial-grade ticketing system. It lets a group of people
intelligently and efficiently manage requests submitted by a community
of users. RT is used by systems administrators, customer support
staffs, NOCs, developers and even marketing departments at over a
thousand sites around the world.

RT3 significantly revamped the RT codebase, featuring standard-compliant
Web UI, approval-based workflow system, REST-powered RPC mail gateway,
recursive group membership with delegates, autoconf, custom field support,
I18N and L10N framework, web-editable scrips, better documentation and
regression test suite, and more.

WWW: http://www.bestpractical.com/rt/