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.
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.).
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.
System Configuration Collector collects and classifies most of your Unix/Linux/BSD configuration data in flat files called snapshots. This allows changes in snapshots of consecutive runs to be detected. These changes are added to a logbook, which is helpful for administrators during troubleshooting and for auditors during audits. Snapshots and logbooks are also available in HTML format. All data can be send to an SCC server, where a Web interface provides access to summaries and supports comparing snapshots of different servers and searching of all data. A WMI-based Windows client is also available.
PowerBroker Identity Services is an application that joins Linux, Unix, and Mac OS machines to Microsoft Active Directory and securely authenticates users with their domain credentials. Features include: joining non-Windows systems to Active Directory domains in a single step from the command line or from a GUI; authenticating users with a single user name and password; enforcing the same password policies for all platforms; supporting multiple forests with one-way and two-way cross forest trusts; caching credentials in case your domain controller goes down; and providing single sign-on for SSH and Putty. It does not require Active Directory schema changes for installation.