Braintree

Bryan Johnson founded it in 2007, and it chased the same developers as Stripe: a clean API, card data that never touched the merchant's own servers, and therefore a much lighter PCI DSS burden. Uber and Airbnb both took their early payments through Braintree.

In 2012 Braintree bought a small payments app called Venmo, and in 2013 PayPal bought the lot for $800 million. Venmo eventually became the better-known name of the two. Johnson spent his share trying to age more slowly, making him one of the few founders whose exit strategy is explicitly not to exit.