A PBX (private branch exchange) is a phone system that switches calls between internal extensions and outside lines. Open-source PBXs are built in two layers:

• Engines do the call handling: Asterisk and FreeSWITCH.
• GUI distributions add web-based management on top of an engine: FreePBX, FusionPBX, Issabel, VitalPBX and others.

Pages¶

• The open-source VoIP/PBX ecosystem in 2026: what's active, what's dead, and recent security history.
• Asterisk: the most widely deployed open-source telephony engine.
• FreePBX: the most popular Asterisk GUI, including a setup and troubleshooting guide.
• Trixbox: a discontinued Asterisk distribution, kept for historical reference.