Venmo is a well known mobile payment app. They also have a service that makes it easier to checkout in other mobile apps by saving your credit and debit cards and allowing you to re-use them later without having to re-type all of the card details, Venmo Touch.
We created a video that communicates the need for this service by showing the frustrations of trying to make a mobile purchase.
update: since this video Apple Pay has come on the scene, but may I ask that you think back before Apple Pay ;)
Venmo has a feature calledVenmo Touch (now PayPal OneTouch) that makes it easier to checkout on your mobile device by saving your credit and debit card information and allowing you to re-use it later with one simple click.