Project Gutenberg, abbreviated as PG, is a volunteer effort to digitize and archive cultural works, to "encourage the creation and distribution of eBooks.
Grooveshark is a service of Escape Media Group Inc (EMG), a Gainesville, FL company. EMG was founded in March 2006 by three University of Florida undergrad students. Sam Tarantino, a "down-on-his-luck economics major", and now CEO of Grooveshark, was on his way to donate plasma when he passed a record store with a sign that said "buy/sell/trade CDs", and had the idea to apply that to digital music.
Pandora is an automated music recommendation service created by the Music Genome Project. Users enter a song or artist that they enjoy, and the service responds by playing selections that are musically similar. Users provide feedback on approval or disapproval of individual songs, which Pandora takes into account for future selections.