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.
liboping is a C library for measuring network latency using ICMP echo requests. It can send to and receive packets from multiple hosts in parallel, which is nice for monitoring applications. Both IPv4 and IPv6 are supported transparently for the programmer and user. A program called oping is included to show the simplicity and potential of the library and provide the functionality at the command line.
Libsmbios is a cross-platform library intended to be used to obtain common information available in a BIOS. Major features include the ability to update the BIOS on Dell systems (in conjunction with the Dell RBU Linux kernel driver), programmatic access to information in SMBIOS tables, and the ability to obtain Dell system-specific information such as the Dell System ID number, service tag, and asset tag. Future plans include APIs for $PIR and mptable mapping. There is a C API for some of the more commonly used functions, and example binaries to show off most of the facilities.
md5i creates an MD5 database of all files in a directory structure and allows you to easily recheck the contents and report if any files have changed. It does not detect removed files, and only computes an MD5 sum if the "last modified" timestamp of a file has changed since the last execution by default. Wrapper scripts for Unix and Windows are included.
memtest86+ is a memory tester which is based on memtest86 v3.0, and provides an up-to-date version of this useful tool, which aims to be as reliable as the original. It has been fixed to work on AMD64 systems, and also properly detects all current CPUs and motherboard chipsets. It supports ECC polling for AMD64, i875P, and E7205, and displays some useful settings for the most popular chipsets.
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.