card.io is a mobile payment service. card.io can be integrated within applications for mobile payments. card.io uses the mobile phone's camera for credit card scanning and payment processing.
The card.io API allows developers to integrate the functionality of card.io with other applications. The main API method is accepting payments and retrieving credit card and payment information.
Without the dot, "cardio" is Rule #1 in Zombieland. With the dot, card.io is PayPal's latest acquisition: the startup formerly known as Lumber Labs, whose technology allows developers to integrate credit card payments into any iOS or Android app with no additional hardware.