FusionPBX is a graphical user interface for FreeSWITCH. It can be used as a high-availability single or domain-based multi-tenant PBX, carrier-grade switch, call center server, fax server, voice-over-ip server, voicemail server, conference server, voice application server, appliance framework and more.
A ClearOS app will be created in the future (likely in 2019, please get in touch if you need sooner). In the mean time: How to install FreeSWITCH on ClearOS
- Impressive guide: https://rtcquickstart.org/guide/RTCQuickStartGuide.pdf