Looks like that link Simon pointed to has the main radius packages listed. Here's a list of packages from Debian related radius usage. Most of them should be available in Ubuntu too as they've been around for a while so probably exist in Ubuntu too. You can find better explanations of these packages by using apt-cache show packagename or by looking up the package name in Synaptic and the highlighting it in the top right window. That will cause an explanation of the package to appear in the bottom right window. One caveat to that is that the apt-cache show method will also give you a listing of all dependencies, software conflicts, suggested and recommended packages to include to get more fully functioning install, etc....
Code:
chillispot - Wireless LAN Access Point Controller
freeradius - a high-performance and highly configurable RADIUS server
freeradius-dbg - a high-performance and highly configurable RADIUS server; debug symbols
freeradius-dialupadmin - set of PHP scripts for administering a FreeRADIUS server
freeradius-iodbc - iODBC module for FreeRADIUS server
freeradius-krb5 - kerberos module for FreeRADIUS server
freeradius-ldap - LDAP module for FreeRADIUS server
freeradius-mysql - MySQL module for FreeRADIUS server
freeradius-postgresql - PostgreSQL module for FreeRADIUS server
hostapd - user space IEEE 802.11 AP and IEEE 802.1X/WPA/WPA2/EAP Authenticator
libapache2-mod-auth-radius - Apache 2.x module for RADIUS authentication
libauthen-radius-perl - user authentication against radius
libauthen-simple-radius-perl - Simple RADIUS authentication
libcrypt-hcesha-perl - Perl extension for one way hash chaining encryption using SHA
libmpfi-dev - multiple precision floating-point interval computation library
libpam-radius-auth - The PAM RADIUS authentication module
libradius1 - /bin/login replacement with RADIUS. Shared lib to used by programs.
libradius1-dev - /bin/login replacement with RADIUS. Header file and link lib.
libradiusclient-ng-dev - Enhanced RADIUS client library development files
libradiusclient-ng2 - Enhanced RADIUS client library
openser - very fast and configurable SIP proxy
openser-radius-modules - radius modules for OpenSER
php-auth - PHP PEAR modules for creating an authentication system
php-radius - Radius protocol implementation in PHP
portslave - Terminal server that does PPP and authenticates via RADIUS
python-pyrad - python module for creating and decoding RADIUS packets
python-smbpasswd - This module can generate both LANMAN and NT password hashes
radiusclient1 - /bin/login replacement which uses the RADIUS protocol for authentication.
radiusd-livingston - Remote Authentication Dial-In User Service (RADIUS) server
ser - Sip Express Router, very fast and configurable SIP proxy
ser-acc-radius-module - contains the ser acc module, with RADIUS support
ser-radius-modules - contains the ser RADIUS modules
xtradius - Free radius server implementation
yardradius - YARD Radius Auth/Acct Server