Contact cards, size as a credit card, contain a single embedded integrated circuit chip. They always come in contact with (inserted into) a reader. Effective for financial transactions, access control, loyalty management, etc. Sometimes the magnetic card is also sort into contact cards.
Memory-only chips are functionally similar to a small floppy disk. They are less expensive than microprocessor chips, while offer less security. So people should not use them to store sensitive or valuable information.