I'm not sure what the first one is, although it is probably some sort of fungal disease.
The second one is a gall, which is a swollen mass of abnormal tissue, that can be caused by fungi, bacteria, or certain insects. In trees, you will often hear these referred to as "burls".
Yes, that is the kind of wood that they use in furniture making, and is quite valuable if you find the right buyer. Most aren't burst open as this one is, but I think it's probably because it is on such a thin tree.