Slide , LinkedIn , Friendster , Rapleaf , Geni.com , Yammer , Yelp, Inc. , Powerset , Practice Fusion , Vator , Palantir Technologies , IronPort , and Votizen . Slide, LinkedIn, Yelp, Geni.com, and Yammer were founded by Thiel's former colleagues at PayPal: Slide by Levchin, Linkedin by Reid Hoffman