Asterisk is a open source communications project that lets you create telephony apps for IP PBXs, VoIP Gateways, etc. Developed by digium
License: Open Source
Asterisk is a well-established open-source PBX system known for its flexibility and extensive community, making it suitable for smaller to medium-sized deployments. FreeSWITCH, on the other hand, is designed for larger-scale applications with advanced features and modular capabilities, making it ideal for complex communication systems.