Buildroot
The Buildroot project website is at http://buildroot.org.
Current versions of Buildroot are capable of building a toolchain, a bootloader (U-Boot, Barebox, GRUB2, or Gummiboot), a kernel, and a root filesystem. It uses GNU make
as the principal build tool.
There is good online documentation at http://buildroot.org/docs.html, including The Buildroot User Manual.
Background
Buildroot was one of the first build systems. It began as part of the uClinux and uClibc projects as a way of generating a small root filesystem for testing. It became a separate project in late 2001 and continued to evolve through to 2006, after which it went into a rather dormant phase. However, since 2009, when Peter Korsgaard took over stewardship, it has been developing rapidly, adding support for glibc
-based toolchains and the ability to build a bootloader and a kernel.
Buildroot is also the foundation of another popular build system, OpenWrt (http://wiki.openwrt.org) which forked from Buildroot around 2004....