PLimit is a security tool to prevent some denial of services on common internet daemons. It will dynamically reject connections from hosts that have already connected too many times on the same service or the same server. IPLimit is fully configurable : you can, for instance, allow 40 connections per second for SMTP, and only 1 per minute for Telnet. It needs the TCPREMOTEIP and TCPLOCALPORT environment variables, so that IPLimit has to be used with a super-server like G2S or TCPServer. You can also use any other inetd variant if you have the tcp-env program (from Qmail). IPLimit was tested on Linux but should work on any other Unix implementation with or without minor changes.
It worth a try: http://www.jedi.claranet.fr/iplimit-0.9.tar.gz