R.Launchpad is a minimal distribution of Linux that builds a system-image from sources into a given disk partition. It covers all the commands needed to boot the most recent version of Linux-2.6.
six-irc is a simple IRC client. It's inspired by sic (from suckless.org), but is more usable and even smaller.
A tool for writing one program which runs on both Python 2.6+ and Python 3.
A standards compliant RTOS with a small footprint.