uClibc (µClibc) is a C library for developing embedded Linux systems. It is much smaller then the GNU C Library, but nearly all applications supported by glibc also work perfectly with uClibc. Porting applications from glibc to uClibc typically involves just recompiling the source code. uClibc even supports shared libraries and threading. It currently runs on standard Linux and MMU-less Linux (also known as µClinux) systems with support for ARM, i386, h8300, m68k, MIPS, mipsel, PowerPC, SH, SPARC, and v850 processors.
ZThread is an advanced object-oriented threading and synchronization library, implemented in C++ for POSIX, MacOS, and Win32 systems. It provides an excellent and powerful abstraction from native threads. It includes interruptible thread objects and several other synchronization control objects.
DirectFB is a thin library that provides developers with hardware graphics acceleration, input device handling and abstraction, an integrated windowing system with support for translucent windows and multiple display layers on top of the Linux framebuffer device. It is a complete hardware abstraction layer with software fallbacks for every graphics operation that is not supported by the underlying hardware.
Puppy Linux is a Linux distribution that is about 100 megabytes, yet it includes a complete set of graphical applications, combined with extensive utility applications. Puppy was created from scratch, file-by-file, optimized for size at every step. Another feature of Puppy Linux is that it can work totally without a hard drive, even allowing you to save data and install extra packages by saving back to the CD or DVD.
Kevux is an operating system based mainly on GNU operating programs and a Linux kernel, all compiled with uclibc instead of the more common glibc. It is not FHS or LSB compatible. Compared to other Linux distributions, Kevux is space efficient (making it suitable for USB disk operation) and difficult to hack into.
Chakra Linux is a Linux distribution that combines the simplicity of Arch Linux with KDE. It is fast, user-friendly, and extremely powerful. It can be used as a live CD or installed to hard disk. Chakra is currently under heavy and active development. It features a graphical installer and automatic hardware configuration. Chakra provides a modular and tweaked package set of the KDE Software Compilation with a lot of useful additions. It features the concept of half-rolling releases and freshly cooked packages and bundles. It is designed for people who really want to learn something about Linux or don't want to deal with administrative overhead.