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.
Square now has an E-commerce API that brings Square services to third party websites. Square is usually associated with its mobile credit card reader and complementary software. With the E-commerce API, merchants can use their own systems with all the benefit of Square's modern payment services.