London's Revolut was founded only three years ago but already has 3 million customers, and is aiming for 100 million customers in the next five years. The challenger bank is set to hit the US market in early 2019, saying 75,000 people are already on the waiting list. "We want to one of the largest financial services companies in the world," says CEO Nikolay Storonsky. A UK app-based banking alternative valued at $1.7 billion has plans to grow even bigger. Just three years old, it's hitting the US early next year to continue its rapid expansion.