FusionPBX

FusionPBX is a web interface to FreeSWITCH that can operate as a highly available single or domain based multi-tenant PBX, a carrier grade switch, a call centre server, a fax server, a voip server, a voicemail server, a conference server, a voice application server and an appliance framework.

That list is not padding, and multi-tenancy is the capability that distinguishes it commercially. A single FusionPBX installation can serve many separate organisations with isolated domains, which is exactly what a service provider or managed service provider needs to sell hosted telephony. Most open source PBX projects are built for one organisation and force a separate instance per customer.

Building on FreeSWITCH rather than Asterisk is the other significant choice. FreeSWITCH was designed later with different concurrency assumptions and is generally considered stronger at high call volumes and at handling many simultaneous media streams, which is why carrier grade switching appears in the description at all.

The feature set is unlimited by licence rather than by tier, covering unlimited extensions, voicemail-to-email, music on hold, call parking, call centre and queues, and phone provisioning, with an editor for provisioning files and FreeSWITCH configuration. FusionPBX explicitly aims to bring corporate level phone system features to small, medium and large businesses alike. It is free and open source with commercial support available.