Introducing the Yocto Project
The Yocto Project is a more complex beast than Buildroot. Not only can it build toolchains, bootloaders, kernels, and root filesystems as Buildroot can, but it can generate an entire Linux distribution for you with binary packages that can be installed at runtime. The build process is structured around groups of recipes, similar to Buildroot packages but written using a combination of Python and shell script. The Yocto Project includes a task scheduler called BitBake that produces whatever you have configured, from the recipes. There is plenty of online documentation at https://www.yoctoproject.org.
Background
The structure of the Yocto Project makes more sense if you look at the background first. Its roots are in OpenEmbedded (https://openembedded.org), which, in turn, grew out of a number of projects to port Linux to various handheld computers, including the Sharp Zaurus and the Compaq iPaq. OpenEmbedded came to life in 2003 as the build system...