Enswitch is a full-featured multi-tenant softswitch for commercial telephony services such as hosted PBX, residential ITSP, SIP trunking, calling cards and more. It scales to tens of thousands of concurrent calls and hundreds of thousands of users on a full redundant cluster. It includes extensive hosted PBX features, prepaid and postpaid billing, invoicing, a web interface for system administrators, resellers, and customers, and a complete JSON API. It’s in production with carriers around the world, from single machine systems running tens of users to systems with several hundred thousand users. It’s also used by enterprises as a corporate PBX where high scalability and redundancy are required, especially across multiple sites.