Lapnet
For the CMS site we wrote our own captive portal (web based authentication) setup to permit users to connect their own machines (e.g. laptops).
We wrote our own (using Linux iptables, ISC dhcpd, Apache/cgi, and a (custom) daemon lapd), since (at the time) none of the existing systems did what we needed, or could easily keep the logs required by the ITS rules. We plan to extend this to Wireless at some point (see Lapwing??) and of course switch to permitting dot1x based (e.g. WPA/WPA2/dot11i) authentication (both for wired and wireless connections).
External Links
Some user documentation can be found at Lapnet, though it doesn't yet mention anything about Raven 'cos we havn't yet re-written all of the docs etc.
For a few more technical details (very out of date and doesn't yet mention Raven), see technical.txt