FreeRADIUS is a high-performance, highly configurable, and feature-rich RADIUS server. Supported features include EAP (wireless authentication, PEAP, TTLS), MySQL, PostgreSQL, Oracle, LDAP, X9.9 token cards, VMPS, and many more. It comes with more than 50 vendor dictionaries, and interoperates with many others. It is the only open source RADIUS server that has implemented EAP, and it is currently deployed in multiple million-user systems.
radiusclient is a framework and library for writing RADIUS clients. The distribution contains a flexible RADIUS aware login replacement, a command line program to send RADIUS accounting records and a utility to query the status of a (Merit) RADIUS server. All these programs are based on a library which lets you develop your own RADIUS aware application in less than 50 lines of C code. It is highly portable and runs at least under Linux, a lot of BSD variants and Solaris.