Lynis is an auditing and hardening tool for Unix derivatives like Linux/BSD/Solaris. It scans systems to detect software and security issues. Besides security-related information, it will also scan for general system information, installed packages, and possible configuration mistakes. The software is aimed at assisting automated auditing, software patch management, and vulnerability and malware scanning of Unix-based systems.
Yet Another Flowmeter (YAF) is a tool for network flow capture, primarily designed to operate efficiently on white box hardware and generate IPFIX flow records. It is designed to operate primarily on Unix-based systems (including Mac OS X), and is supported by the Network Situational Awareness team at CERT.
Gpart is a small tool which tries to guess which partitions are on a PC harddisk in case the primary partition table was damaged. It works by scanning through the device (or file) given on the commandline on a sector basis. Each guessing module is asked if it thinks a filesystem it knows about could start at a given sector. Several filesystem guessing modules are built in, and others can be added dynamically.