CardSpring was a payment platform that enabled developers to create applications and services for credit card-connected offers, loyalty programs, and online-to-offline commerce. It allowed businesses to link web and mobile applications directly to customers' credit or debit cards, facilitating seamless integration for merchant promotions and consumer rewards. CardSpring provided tools for creating and managing card-linked offers while ensuring secure transactions. Please note that CardSpring was acquired by Twitter in 2014, and its services were integrated into Twitter's offerings.