FREEPBX

The "Free" in FreePBX stands for Freedom. That's because FreePBX, the world's most popular open source IP PBX, gives users the tools to build a phone system tailored to their needs... Transform your FreePBX install into a robust Unified Communications system with commercial modules from Sangoma and other add-ons for FreePBX... Visit the Knowledge Base on the FreePBX Wiki! Or let FreePBX experts assist with support for installing FreePBX, updating, troubleshooting, and beyond.