Proteins fold. When it goes wrong, you get cancer. A bunch of people want to know what actually happens in that process so to find a cure. They needed pro supercomputers but they were too cheap. Instead, they invented a program (several I should say) to run on everybody's computer.
An analogy would be like how a person with a terrible computer wanted to convert a HD movie. He just seperated the movie into several chunks and uploaded it. Nice people with good computers downloaded it and converted it and sent it back to him.
As an incentive, he made a point system where bigger chunks are worth more points. People then turned this into a hobby, and thankfully, the movie was HUGE...
GPU folding vs CPU folding is like Badaboom vs Handbrake.
One is for GPU and the other is for CPU.