Open-source SIP User-Agent library

It can be used as a building block for SIP client software for uses such as
VoIP, IM, and many other real-time and person-to-person communication services.
The primary target platform for Sofia-SIP is GNU/Linux. Sofia-SIP is based on a
SIP stack developed at the Nokia Research Center. Sofia-SIP is licensed under
the LGPL.

Homepage:
https://sofia-sip.sourceforge.net/
