Snort is a network intrusion detection and prevention system. It is the most widely deployed technology of its kind in the world. It performs detection using a variety of methods including rules-based detection, anomaly detection, and heuristic analysis of network traffic. Its rules language is open source and available to the public as well.
MultiTail lets you view one or multiple files like the original tail program. The difference is that it creates multiple windows on your console (with ncurses). Merging of 2 or more log files is possible. It can also use colors while displaying the log files (through regular expressions) for faster recognition of what is important. It can also filter lines (again with regular expressions). It has interactive menus for editing given regular expressions and deleting and adding windows. One can also have windows with the output of shell scripts and other software. When viewing the output of external software, MultiTail can mimic the functionality of tools like 'watch'.
GKrellM is a GTK-based stacked monitor program that charts SMP CPUs, disks, load, active net interfaces, and internet connections. There are also builtin monitors for memory and swap, file systems with mount/umount feature, mailbox checking including POP3 and IMAP, clock/calendar, laptop battery, sensors (temperatures, voltages, and fans), and uptime. It has LEDs for the net monitors and an on/off button and online timer for PPP. There is a GUI popup for configuration, plugin extensions can be installed, and many themes are available. It also features a client/server monitoring capability.
ntopmg is a network probe that shows network usage in a way similar to what top does for processes. It acts as a Web server, creating an HTML dump of the network status. It sports a flow collector, an HTTP-based client interface for creating ntop-centric monitoring applications, and RRD for persistently storing traffic statistics. Its C++ core can be scripted in Lua, for changing the appearance and extending functionality.
LogAnalyzer is a Web front-end for syslog and other network event data. It provides easy browsing, searching, basic analysis, and some graphics. Data is taken from databases or plain syslog text files, so LogAnalyzer does not require changes to an existing logging infrastructure. Depending on the log data present, it can process syslog messages, Windows event log entries, and some more exotic things. Its troubleshooting support enables users to quickly find solutions to problems seen in the log data. LogAnalyzer was previously called phpLogCon, and has been renamed since v3.
aircrack-ng is a set of tools for auditing wireless networks. It's an enhanced/reborn version of aircrack. It consists of airodump (an 802.11 packet capture program), aireplay (an 802.11 packet injection program), aircrack (static WEP and WPA-PSK cracking), airdecap (decrypts WEP/WPA capture files), and some tools to handle capture files (merge, convert, etc.).
MIB Smithy is an application for SNMP and COPS developers, MIB and PIB designers, and Internet-draft authors. It provides a GUI-based environment for designing, editing, and compiling MIB and PIB modules according to the SMIv1, SMIv2, and COPS-PR-SPPI standards. It accelerates the development process by providing an easy-to-use GUI-based environment for developing the specifications without the syntax and formatting concerns of editing the modules by hand. It includes a number of built-in basic SNMP management tools, XML support, and (with MIB Smithy Professional) support for custom compiler output formats.