Offhand - no, I don't. Typically, when a motherboard or CPU fails, your computer won't even start. There's little opportunity there for a software testing tool. However, there are cases where you might want to just make sure those two devices are working as they should and not the cause of a small problem.
What about you? Do you know of any free software programs designed to test a motherboard or CPU? I'd love to get some recommendations.