BusyBox combines many common Linux utilities into a small executable. It provides replacements for most of the utilities you usually find in GNU fileutils, shellutils, etc.
BusyBox has been written with size-optimization and limited resources in mind. It is also extremely modular so you can easily include or exclude commands (or features) at compile time. This makes it easy to customize your embedded systems. To create a working system, just add some device nodes in /dev, a few configuration files in /etc, and a Linux kernel.
# cd busybox-1.6.1
# make ARCH=arm CROSS_COMPILE=arm-linux-