OpenSIPS is a mature implementation of a SIP
server/proxy. It is more than a SIP proxy/router,
as it includes application-level functionalities.
OpenSIPS, as a SIP server, can server as the core
component of any SIP-based VoIP solution.
A complete IPsec and IKEv2/IKEv1 implementation for Linux 2.4 and 2.6 kernels.
A portable, fast, light, and extensible IRC client.