MW is a low footprint embedded UI framework core intended for use on very limited systems. It embeds the JPEG, Freetype, and Cairo libraries, so it only depends on X. It should be fairly portable, as the only thing you need is to create a window on every platform and manage the events.
OpenADK is a construction kit for embedded Linux. It creates Linux systems that are optimized for size and short bootup times. The toolchain supports many architectures (arm, m68k, mips, microblaze, ppc, sparc, superh, x86, and x86_64). It can build customized images for Qemu. Raspberry PI, Lemote Yeelong, and Sharp Zaurus devices are supported as a proof of concept. Approximately 685 source packages are available.
yuck is a command line option parser for C that works on a minimal set of dependencies - only a C compiler and the m4 macro processor are required. It supports all the standard use cases: GNU-style long options (--option), condensable short options (-xab for -x -a -b), and optional arguments to long and short options (--foo[=BAR]), multiple occurrence of options (-vvv). Most importantly, it does not depend on libc's getopt() nor getopt_long().