Since most of the modems (DSL/Cable) are using various embedded linux, and the manufacturer support is normally terrible ( they know nothing but copy/paste some stupid FAQ), I suggest we should get a another topic - embedded linux. They have made too much money using open source and but donot provide any valuable support.
BusyBox is one of them, they are widely used in DSL modems. There are a lot, like LynuxWorks: BlueCat, even some other advanced real time linux (like VMOS, applied in aviation applications)
Even OS in I-Phone, the "embedded Max X" for i-phone.