Napster
What: A peer-to-peer file-sharing service that allows people to share MP3s
When: 1999-2001
Why: The sharing of music was illegal under copyright. Many musicians and companies took legal action
Metallica: Was the most famous/vocal of those rallying against it. They had an unreleased, demo version of a song leaked onto it and then played on radio stations.
Spotify: This music sharing took it thoroughly out of the physical realm and into the digital. Clearly, people wanted to have access to music on a large scale. It inspired Spotify, which is well known for paying artists next to nothing for streams.