FreePBX is an open source GUI (graphical user interface) that controls and manages Asterisk (PBX).FreePBX is licensed underGPL.
As an open source, web-based PBX solution, FreePBX is easy to customize and adapt to your changing needs. FreePBX can run in the cloud or on-site, and is currently being used to manage the business communications of all sizes and types of businesses from small one person SOHO businesses, to multi-location corporations and call centers. The FreePBX EcoSystem provides you with the Freedom and Flexibility to custom design business communications around your needs.
You can download the complete iso of FreePBX which includes Asterisk and OS both from the below link
lets talk about installing FreePBX
1. Select FreePBX 5.211.65 with Asterisk 11 ( Full Install )
2. Select the Network type. You can provide IP manually or through DHCP.
3. Select the time zone
4. Set the password for root user.
5. Package installation process will start
6. Installtion will finish and it will restart and ask for root username and password.
You can access GUI from browser