Keybase Chat - End-to-end encrypted chat built into Keybase
Spotify - Map shows when two people play same song at same time
Pithos - pithos is a daemon which provides an S3-compatible frontend for storing files in a Cassandra cluster.
Last.fm - The world's largest online music service. Listen online, find out more about your favourite artists, and get music recommendations, only at Last.fm
Pandora - Pandora Radio is a free (ad-supported) internet radio founded in 2000.
SoundCloud - Enjoy music & follow favourite artists