Here’s a great invention for men who shave their heads. It’s known as the HeadBlade:

As you can see you simply attach the blade to your dominant hand and run it across your head. The reason it’s a good invention is that it takes a past invention (the razer) and improves the process. Apparently the inventor tried to get Gillette and Schick to buy into the idea to no avail. This spurred him on to develop it himself using his own funding and funding from his father and friends. The result is a very successful invention that has sold over 20 million units.