Stannp - Stannp helps to create and send postal Direct Mail campaigns: letters or postcards.
Thankbot - Drive more business with handwritten notes
AmazingMail - Business print-mail solution
Felt for iPhone - Handwritten cards for the modern world
Lob - A simple API to integrate print & mail solutions into your applications.
Handwrytten - Handwritten notes straight from your device. Huge selection of cards or design your own. Handwriting service integrates with 1000's of apps.