Fan Karma helped musicians share fans and promote their concerts, especially while on tour.
As a musician, you could tell a targeted segment of your mailing list about concerts that your fellow musicians are playing.
In return, your fellow musicians promoted your shows to their fans.
It integrated tightly with MailChimp.
Ember and Ember Data on the front end.
Rails and PostgreSQL behind the scenes, providing a nice API.
was fankarma.net (but gone now)
January – July 2013