Library for parsing and validating international phone numbers
Cerberus Content Management System
Java VoIP Softphone (SIP) (replaced by jfPhone)
Open source streamlined SIP client built on Linphone
F-Talk cross-platform p2p encrypted secure voip software
Optimized and cross platform SMPTE 2022 FEC library in C, Python, Java
The OZEKI VoIP Service Checker allows you to check VoIP services.
C++ SIP stack based on Chrome source code