onenetd is a single-server inetd, similar to Dan Bernstein's tcpserver or courier-tcpd from Courier-IMAP. It is small, has been shown to work happily on Linux and Solaris, and supports limiting the number of concurrent connections and refusing further connections with a configurable message (useful for limiting connections to busy FTP servers, for instance). See the included manual page for all the options.
I'm aware the name is hard to spell and pronounce; feel free to suggest a better one!
There is a mailing list for onenetd users and developers, upon which new versions of onenetd are announced and discussed.