There are thousands of arm amputees each year, veterans and non-vets. The one item that has yet to be perfected for amputee fishermen is a one handed knot tyer. Using vest mounted fly pads helps, but it takes a LOT of skill, and the two advertised one-handed hook tyers don't really work very well (just my opinion, but I own them both).
The creator/inventor of a one handed knot tyer will not make a lot of money, but will do a real service to amputee fishermen.
Put on your thinking cap, come up with an idea and post it or do whatever is needed to make it available.