9to5Mac reports this morning that Apples long-rumored fitness and health-tracking app Healthbook is well on its way to reality. Designed to resemble Passbook, the ambitious app will apparently be able to analyze everything from activity and heart rate to blood oxygen levels, though its still unclear what devices or third-party applications will be needed to source the data. 9to5 provides several detailed screenshot recreations that show what Apple is reportedly developing. According to the mocks, Healthbook will use a card interface that surfaces information according to category.