check_multi is kind of a Nagios wrapper plugin which takes advantage of the Nagios 3.x capability to display multiple lines of plugin output. It calls multiple child plugins and displays their output in the long_plugin_output. A summary is given in the standard plugin output. The child return code with the highest severity becomes the parent (check_multi) plugin return code. The configuration is very simple: a NRPE-stylish config file contains a tag for each child plugin and then the check command line.
BigDaddy is a program for monitoring servers. It is similar to Nagios, with the added benefit of also monitoring and controlling the crontab (or any scheduled application) across an entire fleet of servers. The application comes in the form of a daemon for monitoring and reporting as well as an easy-to-use Web-based GUI for controlling monitoring, viewing timelines of incidents, filing incidents and graphing statistics. The application is extensible with any sort of monitoring module and notification is based on a five step escalation process.
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.
iloog is a Gentoo-based live CD targeted mainly at students and scientists. It features UnionFS filesystem support that enables you to write everywhere on the LiveCD and install extra packages, a graphical X environment through the Fluxbox window manager, many programming editors and IDEs, and a plethora of scientific applications, including Octave, Namd, Merlin, and full (La)TeX support.
pwatch is a set of tools for analyzing what a process is doing. Only the "io" command is currently implemented. It presents I/O activity in a nice ncurses screen and allows you to sort by the read/write speed or the number of bytes read/written since the start of the program. It was written to easily detect which program is eating a lot of I/O bandwidth.