Customer.io is a tool that allows businesses to improve their 'lifecycle' or 'timed' ad campaigns, particularly those taking place over email. For example, if a business wants to send emails to customers who've just made purchases recently, or who haven't made purchases for many months, this app provides tools to start, improve and further automate these ad campaigns. In particular, the app aggregates data about customers, which helps better target these email ad campaigns. As one's customerbase grows, this sort of data gathering and automation becomes more and more useful: so too does Customer.io.