Merry-go-round greeting cards have slits cut inside the card allowing it to hold your message on a separate slip of paper.
The person who gets the card can replace the slip of paper with their own and send the card on with a new message. Each card has a refill and instructions.
The makers say the cards have a double environmental benefit because they save the energy required to make a card each time they are re-used and they are made of 100% post consumer recycled stock with green printing processes and soy-based inks.
The cards are sold online singly, or in packets. A packet of six costs about $22.50.