Asterisk.

Open-source PBX framework for building voice and telephony applications

Facts

CM.com
Dutch conversational commerce and communication platform with SMS, voice and payments
NL · commercial
↗
Infobip
Croatian omnichannel communication platform with SMS, voice and chat APIs
HR · commercial
↗
Kamailio
Open-source SIP server for VoIP, WebRTC and real-time communications
DE · open-source
↗
Bird (MessageBird)
Dutch CPaaS platform for SMS, voice, email and chat communication APIs
NL · commercial
↗
NFON
German cloud PBX provider for business communications across Europe
DE · commercial
↗
pascom
German business phone system with unified communications and team messaging
DE · commercial
↗
Sinch
Swedish cloud communications platform for messaging, voice and video APIs
SE · commercial
↗
sipgate
German VoIP provider offering business phone systems and SIP trunking
DE · commercial
↗