"Here we'll take a look at six different open and free Remote
Authentication Dial In User Service (RADIUS) servers available for
Linux (and other platforms). You'll find something that will work
for you, whether you're supporting dial-up or VPN users, offering
802.1X for Wi-Fi security, or running VoIP. All your
Authentication, Authorization, and Accounting (AAA) needs can be
met on a Linux server.
"The FreeRADIUS project was founded in June of 1999 by Miquel
van Smoorenburg and Alan DeKok. Its freely available via the GNU
General Public License, Version 2 (GPLv2) for running on Linux,
other Unix-like systems, and even Windows. Since the first stable
release in 2001 there have been feature improvements and bug fixes
released every couple of months. There is extensive community
support via documentation, a Wiki, mailing lists, and tutorials
throughout the Internet. Commercial support is also available from
consulting firms like Network RADIUS."