Open Source RADIUS Servers

In alphabetical order. To be listed here, email webmaster@freeradius.org.

Cistron
The server which has become widely used in the free software community. Written by Miquel van Smoorenburg (miquels@cistron.nl) from the original Livingston source. The server is not actively maintained, and the mailing lists are quiet.
GNU Radius
Yet another Cistron variant. Much of the code has been rewritten. Lex and Yacc are used extensively. The re-write configuration file is very useful. There has not been a release in two years, however.
FreeRADIUS
The worlds most popular RADIUS server. Actively maintained, with an active mailing list.
JRadius
A Java plugin for FreeRADIUS, which talks to a Java server, allowing you to write RADIUS handlers in Java.
ICRADIUS
A variant of Cistron, with MySQL support, and a web-based front end. It does not appear to be actively maintained.
OpenRADIUS
A completely new server implementation, where everything is pluggable modules, completely under the control of the administrator. It is actively maintained, and in some ways is more configurable than FreeRADIUS.
XtRADIUS
Another Cistron variant, with extensions for running external programs for accounting or authentication. It does not appear to be actively maintained.
YARD RADIUS
Is derived from the open sources of Livingston Radius Server 2.1. It has better configuration support, and extended features. It does not appear to be actively maintained.