Asterisk - An open source telephony switching and private branch exchange service for Linux.
3CX - Hosted PBX with CRM integration and mobile apps
JustCall - The Cloud Phone System of choice for modern sales and support teams. We help end clueless conversations by adding context to every call.
CallHub - Predictive Call Center, Voice and Text Broadcasting app
Dialpad - Switch is a cloud-based phone system built for Google Apps users.
Cloud Telephony - Cloud Telephony delivers automated telephone applications to any phone, any place, anytime.