Here's one I haven't seen before:
It's the motherboard from a Toshiba Satellite Pro M15-S405 laptop. The brown crud is probably flux left over from the soldering operation or something corrosive, that was trapped between the PCB and a thin plastic "protective" covering under the DVD drive. The board acts totally dead. No power, no charge lite, no sounds, no nothing. At first, I thought that someone had spilled some liquid into the laptop. Nope, because all the corrosion is BETWEEN the PCB and the plastic, with nothing on top of the plastic. The plastic covering was totally clean. There's no corrosion in the area that's NOT under the "protective" covering, so it seems whatever did the damage, was volatile.
The customer has 3 other identical laptops. I just inspected them (through the DVD slot), and found no corrosion.
I'm not sure I'll be able to fix this one as the rotted traces in this area are very tiny. It's probably not worth the effort for a 9 year old laptop.