Giftbit Payment API - Stripe for gift cards
Postsnap - Postsnap's iPhone app is the best, free postcard creator. Make & send real printed postcards, greeting cards, invitations and announcement cards using your own photos.
Raise - The easiest way to save money on the go
The Simple Postcard - Text a photo to mail it as a postcard
Gemnote - Handwritten cards & premium custom gifts for companies
Felt for iPhone - Handwritten cards for the modern world