memtester is a user-space utility for testing the memory subsystem in a computer to determine if it is faulty. It does a good job of finding intermittent faults and non-deterministic faults. It has many tests to help catch borderline memory. memtester should compile and run on any 32- or 64-bit Unix or Unix-like system.
SystemRescueCd is a Linux system available from a bootable CDROM that provides an easy way to perform administrative tasks on your computer, such as creating and editing the partitions of the hard disk or backing up data. It contains a lot of system utilities (such as parted, partimage, and fstools), and basic programs (such as editors, midnight commander, and network tools). It also includes GParted, a Partition Magic clone that makes editing partitions easy with its graphical user interface. This CDROM aims to be very easy to use and accessible to everybody, and it also provides advanced personalization features.
INSERT (the Inside Security Rescue Toolkit) aims to be a multi-functional, multi-purpose disaster recovery and network analysis system. It boots from a credit card-sized CD-ROM and is basically a stripped-down version of Knoppix. It features good hardware detection, fluxbox, emelfm, links-hacked, ssh, tcpdump, nmap, chntpwd, and much more. It provides full read-write support for NTFS partitions (using ntfs-3g), and the ClamAV virus scanner (including a fairly recent signature database and a GUI). It provides partition handling with gParted and also has a network boot facility.
Ultimate Boot CD is a collection of Freeware and Free Software tools for PC diagnostics and maintenance. Included are tools for BIOS editing, CPU and memory testing, boot management, data recovery, peripheral and system inventory, and hard drive partitioning, cloning, wiping, diagnostics, and low-level editing. All tools boot and run from the CD.
FTPL (FakeTime Preload Library, aka libfaketime) intercepts various system library calls and tricks programs of your choice into seeing a faked system time without having to change the time system-wide. This can be used for running legacy software with Y2K bugs, testing software for year-2038 compliance, debugging time-related issues such as expired SSL certificates, and using software that ceases to run outside a certain time frame. The faked time can be specified either absolutely or relative to the real current time, and optionally also affects file timestamps. The faked clock continues to run, but can optionally be frozen, slowed down, or made faster. A wrapper script "faketime" simplifies the usage, similar to tools such as fakechroot.
picocom is a minimal dumb-terminal emulation program. It is ideal for embedded systems since its memory footprint is minimal (less than 20K, when stripped). Apart from being a handy little tool, the source distribution includes a simple, easy to use, and thoroughly documented terminal-management library.
Kernel Security Checker is a useful tool to locate attackers residing within a system by employing a direct analysis of the kernel through /dev/kmem and bypassing the hiding techniques of the intruder (kernel static recompilation or use of LKMs). It can find the modified syscalls from userspace, detect the promiscuous interfaces, and find the modifications applied to a protocol.