A web server logfile analyzer that works as a CGI and/or from command line, and supports multiple languages. (Perl)

Resolves IP numbers to hostnames like in Apache, Squid, or other logfiles. It is able to cache lookups in a file. (Perl)

A general purpose monitoring engine for use by home users and system administrators (Perl) [Unix, Win32]

Emails a report of all packets that have been logged by the kernel's ipchains or iptables packet filtering subsystems. (Perl) [GNU/Linux]

A network load monitoring applet for GNOME. (C) [GNU/Linux, FreeBSD]

Ngrep is a pcap-aware tool that will allow you to specify extended regular expressions to match against data part of packets on the network. (C) [GNU/Linux, BSD, Windows 95/98/2000]

A network interface traffic statistics reporting and graphing tool. (PHP)

Assists in visualizing a Data Center's computer rack layouts by creating a web page with HTML tables to show a frontview of the racks. Included are brief commandline and CGI scripts to demonstrate its implementation. (Perl) [Linux]

Software for application and network monitoring - logging, monitoring, capacity planning, availability and performance measurement, and helpdesk information. (C, PHP) [POSIX]