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.
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.
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.).
Big Brother is a combination of monitoring methods. Unlike SNMP where information is just collected and devices polled, Big Brother is designed in such a way that each local system broadcasts its own information to a central location. Simultaneously, Big Brother also polls all networked systems from a central location. This creates a highly efficient and redundant method for proactive network monitoring.
bandwidthd tracks usage of TCP/IP network subnets and builds HTML files with graphs to display network utilization. Charts are built by individual IP to show their utilization over 2, 8, 45, and 400 day periods. It color codes HTTP, HTTPS, TCP,UDP, ICMP, VPN, and P2P traffic. Unlike MRTG, it tracks each individual IP address and subnets, not the status of any particular link. Static mode is fast and easy to set up and has few dependencies. Database mode supports filtering by subnet, multiple sensors, custom reports and intervals, and can process thousands of IPs efficiently. Network utilization can be logged in CDF or a backend database.
Lire is a pluggable log analyzer. It has analyzers for over 25 log file formats, ranging from Apache WWW log files to iptables firewall logs and CUPS printing logs. Reports are generated in 9 different output formats, ranging from Excel 95 to PDF to HTML, optionally with included graphs.
MIB Smithy SDK is a dynamic extension to Tcl/Tk (8.4+) that allows development of custom scripts for controlling SNMP agents, manipulating SMI definitions, doing conversions, and more. It is based on the core of Muonics' MIB Smithy, and the SDK supports SMIv1 and SMIv2, as well as SNMPv1/v2c/v3 with HMAC-SHA-96 and HMAC-MD5-96 authentication and DES/CBC and AES128/CFB privacy. It also provides complete read-write access to all elements of SMI/MIB Module definitions, unlike similar extensions that provide only read access to a limited subset. The SDK allows multiple discrete SMI databases and SNMP sessions, and provides all of the built-in validation and error recovery capabilites of the full product, without the visual MIB development environment.