osTicket

osTicket is a popular open-source ticketing system that can be downloaded and installed on your own servers for free. It provides a basic but functional web-based customer support platform with email integration, a help center, and customizable ticket filters and workflows.

It relies on community support and custom development for advanced features. It is targeted at tech-savvy individuals, small businesses, or organizations with strict budget constraints who need internal control over their data. It ranks for being a completely free, self-hosted option that delivers core ticketing functionality reliably.