execline is a very light, non-interactive scripting language, which is similar to a shell. Simple shell scripts can be easily rewritten in the execline language, improving performance and memory usage. execline was designed for use in embedded systems, but works on most Unix flavors.
skalibs is a set of general-purpose, low-level C libraries, all in the public domain. It can replace or hide the standard C library to some extent. It is designed to allow building of small static binaries. It is used in building all skarnet.org software, including execline and s6.
superseriousstats is a small and efficient program for creating a Web page with statistics from various types of IRC logs. It keeps track of its parse history and only processes new activity before storing any accumulated data in a SQLite or MySQL database. It is suitable for high volume IRC channels and large log archives, and is relatively easy to integrate with IRC services (e.g. bots) that interact with the database and provide last seen information and many other statistics directly in your channel.
s6-portable-utils is a set of tiny general Unix utilities, often performing well-known tasks such as cut and grep, but optimized for simplicity and small size. They were designed for embedded systems and other constrained environments, but work everywhere. Other sets of small utilities are usually system-specific; for instance, the (otherwise excellent) BusyBox project only works on Linux.
Micro Tetris is based on the 1989 International Obfuscated C Code Contest Best Game entry. It is a very small implementation, with extreme similarity to the BSD Tetris implementation. So it is very suitable for small embedded systems with only serial or SSH console access. The code uses no curses or other heavy libraries, only ANSI escape sequences and the Unix "stty" command to setup and restore the display.
exude is a simple to use memory debugger. It enhances standard memory allocation calls with simple replacements that add just a little more functionality, such as keeping track of whether memory was previously allocated, and prevents common errors such as double frees, memory leaks, and so on.