- Napster (1999-2001)
Launched by a 19-year-old Parker and pal Shawn Fanning, then 18, the service enabled music fans to share MP3s — and before it was shut down by court order, it exposed the recording industry's vulnerability to technological change. (Music-industry revenue in 2015 was down 44% from its 1999 peak.)
- Plaxo (2002-04)
An automated online contact-management service, now owned by Comcast, that relied (controversially) on viral marketing to grow.
- Facebook (2004-05)
Parker met Facebook's founders during its infancy. As president, he helped Facebook enlist its first major investor (Peter Thiel) and develop its user interface.
- Spotify (2010-Today)
Parker made an early investment in the Swedish music-streaming service, then helped it negotiate revenue deals with record labels.
- Airtime (2011-Today)
Airtime, a free videochat service, petered out amid industry ridicule, but Parker continues to champion the idea, and a relaunch looms.
- Brigade (2014-Today)
The self-styled "social network made for politics" sends voting guides and go-to-the-polls reminders to users of its app.
- The Screening Room (2016-Today)
Parker's new venture will offer a $150 home set-top box that lets users watch day-of-opening movies at home for $50 apiece. Theater owners fear it could be their Napster. Some movie-makers see it as their industry's salvation.