There are several implementations for XTACACS and TACACS+ daemons. The following lists those I know.
public domain
C source code
public domain
TACACS, XTACACS
access lists, discriminate by NAS and line, limit number of logins, time-dependant login
C source code
public domain; reference implementation without support
TACACS+
account expiration, pre- and port-authorization scripts, support for S/Key
C source code
The source code is export controlled.
commercial
TACACS+
account expiration, time-dependant login, discriminate by NAS, allow password change, GUI
Binary
Cisco sales channels
SunOS4, SunOS5
commercial
RADIUS, TACACS+
?
binary
Windows 95, Windows NT, UNIX
Originally developped by Universal Networks
commercial (in beta as of 1996-10-03)
TACACS, XTACACS, RADIUS
binary
Windows NT
commercial
Support for One-Time password using SecureID card
binary
Rick Wagner <rwagner@ngwmail.ais.umn.edu>
Dave Safford <Dave.Safford@mpn.cp.philips.com>
commercial
TACACS+
GUI, account expiration, login hours restriction, time/traffic credit restriction, time quotas, discriminate by NAS, NAS port or Caller ID, max concurrent logins, Remote Manager/Console, kill users (via RSH)
binary
Windows NT, Windows 95