Buildroot
Buildroot is a set of Makefiles and patches that simplifies and automates the process of building a complete and bootable Linux environment for an embedded system, while using cross-compilation to allow building for multiple target platforms on a single Linux-based development system. Buildroot can automatically build the required cross-compilation toolchain, create a root file system, compile a Linux kernel image, and generate a boot loader for the targeted embedded system, or it can perform any independent combination of these steps. For example, an already installed cross-compilation toolchain can be used independently, while Buildroot only creates  the root file system. Buildroot is primarily intended to be used with small or embedded systems based on various computer architectures and instruction set architectures (ISAs), including x86, ARM, MIPS and PowerPC. Numerous architectures and their variants are supported; Buildroot also comes with default configurations for several off-the-shelf available embedded boards, such as Cubieboard, Raspberry Pi and SheevaPlug. Several third-party projects and products use Buildroot as the basis for their build systems, including the OpenWrt project that creates an embedded operating system, and firmware for the customer-premises equipment (CPE) used by the Google Fiber broadband service . Multiple C standard libraries are supported as part of the toolchain, including the GNU C Library, uClibc and musl, as well as the C standard libraries that belong to various preconfigured development environments, such as those provided by Linaro. Buildroot's build configuration system internally uses Kconfig, which provides features such as a menu-driven interface, handling of dependencies, and contextual help; Kconfig is also used by the Linux kernel for its source-level configuration. Buildroot is organized around numerous automatically downloaded packages, which contain the source code of various userspace applications, system utilities, and libraries. Root file system images , which are the final results, may be built using various file systems, including cramfs, JFFS2, romfs, SquashFS and UBIFS. Buildroot is free and open-source software, maintained by Peter Korsgaard and licensed under version 2 or later of the GNU General Public License (GPL). The project started in 2001, with initial intentions to serve as a testbed for uClibc. New releases are made available every three months.