openSIPS

OpenSIPS is a GPL‑licensed SIP server that functions as a proxy and application platform for voice, video, instant messaging, presence and other SIP‑based extensions. It is designed for self‑hosting and is available under an open‑source, libre license without subscription requirements. The software is positioned for carriers, telecom operators, IT service providers and enterprises that need high‑throughput signaling, supporting tens of thousands of calls per second and millions of concurrent sessions.

The core provides a flexible routing script language and a large collection of more than 120 modules, enabling custom routing logic, integration with back‑end systems, and implementation of services such as Class 4/5 residential platforms, trunking, virtual PBX, session border control, load balancing, IMS gateways and call‑center solutions. A stable release series (3.6.x) and a newer 4.0 beta introduce redesigns for TCP/TLS handling, multi‑threaded I/O, bond sockets and proxy‑protocol support.

Documentation, module listings, tutorials and community mailing lists are provided for installation, development and business use. Continuous integration, unit testing, OSS‑Fuzz and security audits are part of the project’s development workflow, and a control‑panel UI is available for managing OpenSIPS instances.