These are the individual projects that make up the Yocto Project. Each of these holds a key role in developing embedded Linux, and the Yocto Project works to make all of them interoperable and useful.
Matchbox is an Open Source base environment for the X Window System running on non-desktop embedded platforms such as handhelds, set-top boxes, kiosks and anything else for which screen space, input mechanisms or system resources are limited.
Matchbox consists of a number of interchangeable and optional applications that can be tailored to a specific non desktop platform to enhance usability in a 'constrained' environment.
Find the Matchbox sources on http://git.yoctoproject.org/