open-source

Zulip is a powerful open-source team chat application that combines the immediacy of real-time chat with the organization of email-style threading, designed for productive team collaboration.

Pretix is a ticket sales platform for events that provides a comprehensive solution for selling tickets online and at the door with a focus on data privacy and flexibility.

Fusio is an open-source API management platform which helps to build and manage REST APIs. Built with PHP, it provides comprehensive API development, documentation, and management capabilities with a focus on developer productivity and API governance.

Revolt is an open-source, self-hostable chat platform designed as a privacy-focused alternative to Discord, featuring text/voice channels, customizable servers, and a familiar user interface without compromising on user privacy.

Koha is the world's first free and open-source integrated library system (ILS). It provides enterprise-class features including acquisitions, circulation, cataloging, label printing, offline circulation, and comprehensive patron management for libraries of all sizes.