The GNU Gatekeeper is a free H.323 gatekeeper based on the OpenH323 project. You can use it to manage a Voice-over-IP network and let endpoints (e.g., Netmeeting) communicate through symbolic names. It also has an external interface for billing and other applications. It runs on a number of Unix versions (including Linux and Solaris) and Windows.
NetPlug is an extensible multi-connections, multi-protocol, network client program, written in pure Tcl/Tk. Includes a complete Irc client plug in that you should love if you like IrcII 'classic' look & feel (plus customizable style/colors scheme, sound,... Now includes full DCC support (with GUI), ircII like aliases and improved scripting (Tcl!), keywords (your nick...) highlighting, and more
The netpipes package makes TCP/IP streams usable in shell scripts. It can also simplify client/server code by allowing the programmer to skip all the tedious programming bits related to sockets and concentrate on writing a filter/service. <P>Applications of these utilities can include file transfer, network backups, HTTP queries, remote procedure calls, and TCP daemon testing. <P>The SSL encryption filter available in the US/Canada version can be applied by shell scripts communicating with secure HTTPDs and can be used to make an SSL IMAPD out of a non-SSL one. (requires the SSLeay library).
Angel is a simple yet useful tool to monitor the services on your network. Technically speaking, it's a Perl program that runs every 'n' minutes (usually fired from your cron) and calls different perl subprograms (referred to as "plugins" from now on) to do the actual testing. It will then generate an HTML table containing the status of your network.
pmacct is a small set of passive network monitoring tools to account, filter, classify, aggregate, and export IPv4 and IPv6 traffic. A pluggable and flexible architecture allows storing collected network data in memory tables, RDBMSs (MySQL, SQLite, PostgreSQL, BDB), and flat files, and also export via IPFIX, NetFlow, or sFlow protocols to remote collectors. pmacct features fully customizable historical data breakdown, sampling, BGP correlation, tagging, and triggers. Libpcap, ULOG, sFlow v2/v4/v5, NetFlow v1/v5/v7/v8/v9, and IPFIX are supported data capturing methods.
Dialback is a set of html pages and some bash scripts to enable a host to call you back and set up a ppp link. It also includes a MS Windows dial-up networking script should you wish to use such a machine for a client. It is intended for legitimate remote access where you need good security (ppp link only available on return call) and/or the other end is willing to foot the bill for your connection time. Please note that it should be fairly to set up other protocols such as slip.