FreeRADIUS is an open source RADIUS server.
It is the most popular and widely used RADIUS server in the world, with over one million downloads of every released version.
RADIUS servers authenticate users and apply authorisation policies when they sign into a service.
RADIUS is commonly used as the authentication for Wireless, 3G, Broadband, Terminal login (to servers), Wired network ports, and web applications. It's also used to log information about data usage and commands issue.
FreeRADIUSes key features are its speed, its reliability, its ease of integration, and its simplicity. It's main competitors are Microsoft's NPS, Cisco ACS, Radiator and Juniper steel belted RADIUS.
The end goal of the project is to develop something that integrates multiple elements of network control, from DHCP to DNS as well as RADIUS.
The server is used by Network and Software engineers, but CTOs higher level managers are the ones who make the decision to choose it over a commercial solution.