OpenWRT

OpenWRT is essentially a Linux distribution for embedded systems, specifically routers. It has an incredibly modular structure which allows it to build easily for dozens of different devices and makes package selection easy. It also makes browsing around its source relatively difficult. When you first download a copy of "White Russian", the stable branch of OpenWRT, you don't have a linux kernel, or even a toolchain, but you have its unique build system, which is everything you need to build a firmware image. As far as we can tell it:

• Downloads the correct toolchain
• Builds the toolchain
• Downloads a linux kernel
• Downloads your selected packages
• Uses the toolchain to build the kernel / packages
• Smushes everything together into several flavors of executable (depending on which file system you desire)
• Also creates versions with proper Linksys headers so that they can be uploaded though the web interface as "legit" firmware upgrades

So though the precious bounty is not in the original download, once you complete the build process, the build system leaves the linux source behind in the build_mipsel directory, and the toolchain is left waiting to be swiped as well.