Request Tracker
Request Tracker (RT) is the system you need to track the important tasks you can't afford to forget. The open-source enterprise grade self-hosted (or cloud hosted) ticketing system
he source code and API are completely open! You are free to customize RT and integrate with other systems and tools. You also aren’t locked into a vendor and you never need to worry about paying for software licenses.
requesttracker.io
Software is used by GNU/Linux Debian