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.
asapm is an AfterStep look & feel Advanced Power Management (APM) monitor for laptop and notebook PCs running Linux or FreeBSD/NetBSD/OpenBSD and X Windows. It displays charge left in the battery, the time left to the total discharge of the battery, computer is connected to the mains or is working on a battery and the battery status high/low/critical.
Spong is a simple system-monitoring package. It features client-based monitoring (CPU, disk, processes, logs, etc.), monitoring of network services, grouping of hosts (routers, servers, workstations, and PCs), host-specific contact and downtime information, configuration on a client-by-client basis, results displayed via the Web, history of problems, messaging (via email or pager) when problems occur, and verbose information to help diagnosis problems. It communicates via simple TCP-based messages, and is written in Perl.
Trinux is a minimal Linux distribution that boots from a single floppy or CD-ROM, loads its packages from an FTP/HTTP server, IDE filesystem, or additional floppies, and runs entirely in RAM. It contains the most comprehensive set of network security tools available in any Linux distribution and can be used to conduct security research, analyze network traffic, and perform vulnerability testing of networks and applications.
The NET-SNMP (formerly UCD-SNMP) package contains various tools relating to the Simple Network Management Protocol including an extensible agent, an SNMP library, tools to request or set information from SNMP agents, tools to generate and handle SNMP traps, a version of the unix 'netstat' command using SNMP and a Tk/perl mib browser. It was originally based on the Carnegie Mellon University SNMP implementation (version 220.127.116.11), but has been greatly enhanced, ported and fixed and barely resembles the original package anymore.
ipac is an IP accounting package for Linux. It collects, summarizes, and nicely displays IP accounting data. The output of ipac can be a simple ASCII table, an ASCII graph, or even images with graphs showing traffic progression. ipac can be used for IP traffic analysis and for accounting purposes.
Xlogmaster allows comfortable and fast control of all the important system logfiles and devices that are readable via cat (/proc/XYZ for instance). Filters allow to raise/lower/hide lines. Due to usage of the GTK+ toolkit and full runtime configurability the user can modify the appearance of the xlogmaster to whatever fits his desktop best.