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 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).

NoCatSplash is the successor to NoCatAuth, which was written in Perl. NoCatSplash is written in multi-threaded ANSI C in order to be smaller and work better on embedded style devices.

You can get it from:
http://nocat.net/download/NoCatSplash/

Instructions for building NoCatSplash with uClibc are included in the distribution in the README.uClibc file. A recent build against uClibc yielded an executable that was only 120k in size, and depended on nothing beyond libc.so and libpthread.so. As you can see, it doesn't require perl, and hence should be slim enough to run on OpenAP, LEAF distros, and other embedded-style Linux platforms.

Currently, only open mode and iptables are supported. Authenticating modes are slated to be added shortly, as well as support for OpenBSD and FreeBSD.

We could really use your help beta-testing this. Please send me bug reports personally, as our Request Tracker install is still incomplete.