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.
innotop is a MySQL and InnoDB monitor that lets you view and manage what's happening inside your MySQL servers. Features include a top-like query list, a top-like InnoDB transaction list, and much more. This tool gives you a high level of insight into the inner workings of InnoDB.
iogen is an I/O generator. It forks child processes that each run a mix of reads and writes. The idea is to generate heavily fragmented files to make the hardware suffer as much as possible. This tool has been used to test filesystems, drivers, firmware, and hardware devices. It is by no means meant as a performance measuring tool since it tries to recreate the worst case scenario I/O.
lcdtest is a utility to display monitor test patterns. It was originally written for use with LCD monitors, and may be useful in finding pixels that are stuck on or off as well as for adjustment (automatic or manual). However, it can be useful for CRT monitors as well. lcdtest uses the SDL library, and has been used on Linux with X and on Windows, but may work on other platforms supported by SDL.
The libexplain project provides a library that may be used to explain Unix and Linux system call errors. This will make your application's error messages much more informative to your users. The library is not quite a drop-in replacement for strerror, but it comes close: each system call has a dedicated libexplain function.