Answer: Napster

MP3, the now ubiquitous music format, took a halting twelve year journey from its invention to widespread adoption. Invented in 1987, the compressed music format didn’t see much use outside of highly computer-literate circles for most of the 1990s. Very small groups of music enthusiasts in IRC chat channels and Usenet music groups swapped tracks they had either personally ripped or collected, but the total volume of music trading and MP3 distribution was low.

All of that changed with the 1999 introduction of music sharing service Napster. Napster was a peer-to-peer file sharing service that made it extremely easy to share your entire music collection and, in turn, browse the huge database of music being shared by millions of other users. At the peak of its popularity in early 2001 Napster had roughly 25 million users sharing 80 million tracks.

While the service was wildly popular among file traders it was particularly unpopular among record companies and college IT departments. The former successfully campaigned to shut the service down in light of the rampant copyright infringement and the latter did their best block the service on campuses–Napster-driven file trading routinely consumed over half the available bandwidth on college campuses. Napster was active from June of 1999 until July of 2001 and, legality of the venture aside, was pivotal in ushering the age of digital music.