18. Shawn Fanning - Napster 
Shawn Fanning developed Napster, a peer-to-peer file-sharing program designed to let music fans find and trade music. Users put whatever files they were willing to share with others into special directories on their hard drives. The service had more than 25 million users at its peak in 2001, and was shut down after a series of high-profile lawsuits, not before helping to spark the
digital music revolution now dominated by Apple. Napster has since been rebranded and acquired by Roxio.