ticketing

GLPI is a Free Asset and IT Management Software package, Data center management, ITIL Service Desk, licenses tracking and software auditing.

Zammad is a web based open source helpdesk/customer support system.

FreeScout — Free self-hosted help desk & shared mailbox (Zendesk / Help Scout alternative)

Attendize is an open-source ticket selling and event management platform built on Laravel.

Helpy is a modern, open source helpdesk customer support application. Features include knowledgebase, community discussions and support tickets integrated with email.