Buildroot
"Buildroot is a set of Makefiles and patches that allows to easily generate both a cross-compilation toolchain and a root filesystem for your target. The cross-compilation toolchain uses uClibc (http://www.uclibc.org/), a tiny C standard library. [...]
As said above, Buildroot is basically a set of Makefiles that download, configure and compiles software with the correct options. It also includes some patches for various software, mainly the ones involved in the cross-compilation tool chain (gcc, binutils and uClibc)."
Resources: