NoCatSplash is the successor of NoCatAuth, rewritten in multi-threaded ANSI C in order to be smaller and work better on embedded style devices.
(From the README)
NoCatSplash is a Open Public Network Gateway Daemon. It performs as a captive/open/active portal. When run on a gateway/router on a network, all web requests are redirected until the client either logs in or clicks "I Accept" to an AUP. The gateway daemon then changes the firewall rules on the gateway to pass traffic for that client (based on IP address and MAC address).
A version of NoCatSplash compiled for the LinksysWrt54G can be founded at http://nocat.net/~rob/wrt54g/
There are many people looking for more information to get nocatsplash installed on the WRT54G using alternative firmwares. What is the compatability with OpenWRT, Sveasoft, and the others? What about the official Linksys firmware? The reason is that people would like to filter protocols and also throttle/prioritize packets. Nocatsplash is ideal in a public environment. But it lacks the packetshaping and protocol filtering required for such a configuration. If anybody has more information of using nocatsplash in these types of configurations please post information here.
Go to http://nocat.net/ and check out the mailing list. Passive mode (authed access) is working, but Throttling/Prioritization is not in the code, it could be added (patches are always welcome). Cross-compiling the latest source with your OpenWRT/ewrt toolchain shouldn't be a big deal if you've got one set up.
It's unlikely the 'official' firmware will come with NoCat.