The typical Inetd daemon has some drawbacks, so replacements have been created. One is tcpserver, another is xinetd.
Ucspi's tcpserver is available here:
http://cr.yp.to/ucspi-tcp.html
Xinetd is available here, and ships with most Linux distributions:
Tcpserver allows a default of 40 concurrent connections, (an adjustable parameter), and does source address checking. It stores it's wrapper information in a binary database to speed up reads of the information.
Xinetd has libwrap compiled in, and connection rate limiting features to thwart denial of service attacks. It also has nicely configurable logging capabilities. Xinetd is the default inetd in most Linux distributions.
We use tcpserver to run the Smtpd daemon for Anti-Relay functionality on A.S.C's mailservers. Here is some of the tcp.smtp file that is converted into a binary database format for actual use on A.S.C.'s mailserver:
129.19.64-79:allow,RELAYCLIENT=""
127.:allow,RELAYCLIENT=""
:deny,RELAYCLIENT="Relaying
denied. If you are a local user, contact Computing Services"
Check man tcpserver xinetd xinetd.conf and the files in /etc/xinetd.d