Yate is a softswitch (concept of separating the network hardware from network software).
It supports VoIP protocols: H.323, SIP, IAX1, IAX2, RTP. For the plain old telephony systems (PSTN) it supports ISDN BRI and PRI. Is compatibile with EuroISDN, National ISDN, Lucent 5E, Nortel DMS-100, NI-2.
Yate can be used for:
VoIP (SIP, H323, IAX) - PSTN gateways
PC2Phone prepaid or postpaid calling systems
Calling card applications
The software is written in C++ and it supports scripting in various programming languages.
YATE's license is GPL with an exception for linking with OpenH323 and PWlib (licensed under MPL).