WhoISP

Radius
AAA Radius Server (Merit) - Merit has gone commercial.
Cistron - Cistron RADIUS is an authentication and accounting server for terminal servers that speak the RADIUS protocol. (free)
Compiling Livingston RADIUS 2.1 under RedHat Linux 6.x - Howto
DTC Radius - The DTC Radius ver 2.03 is based Ascend Radius, and added some DTC original features include some Livingston RADIUS 2.0.1 features. (free)
Emerald Radius - RadiusNT and RadiusX for Linux/Solaris/Cobalt can manage remote user access on multiple linked networks containing RADIUS compliant network access and/or security devices. (commercial)
NavisRadius - From Lucent. Powerful, and expensive.
NetReg - NetReg is an automated system that requires an unknown DHCP client to register their hardware before gaining full network access. Through a simple web interface, the client is prompted for their user identification.
Radiator - Radiator is the highly flexible, configurable and extensible Radius server from Open System Consultants. (commercial)
Radius Report - RadiusReport is a radius log analysis program written in perl. It will allow you to produce many, varied, types of reports from one or several radius log files.
Steel Belted Radius - RADIUS/AAA server that lets you centralize the authentication of all your remote users, and track and document all remote access activity. (commercial)
The FreeRADIUS Server Project - The FreeRADIUS Server Project is an attempt to create a high-performance and highly configurable GPL'd RADIUS server. It is generally similar to the Livingston 2.0 RADIUS server, but has a lot more features, and is much more configurable.
The Port Master Monitor Utility (PMMON) - Monitors your portmasters for multiple logins, controls time limits on a user's login sessions both hard and soft limits. Kicks user off of your terminal server for idleing too long, or having a low average byte transfer.