Intriguing. What would HN think of an API for physically printing and mailing things? i.e., an API where you pay ~$0.50 per postcard, and it is printed and deposited in the mail autonomously. You could use it for CRM applications, address verification (like Google Adwords), etc
Not exactly the same thing, but I am building a site for my wife to do custom greeting cards. It's not really at a stage where it is designed to be used automatically, but if someone was interested, we'd be willing to look at it.
The current site is the product of a couple days of teaching myself how to use Stripe, Bootstrap, and PHP, since I'm not really a web developer.
A few API's like this have been posted (ha) before. I investigated this just a little bit since at one time I had an idea that upload a postcard image and mail it to anywhere in the world but I never really found something I liked.
I'd use it, especially if you can somehow connect it to HelloSign. This is something older people really need, at least from my limited view of my grandparents. They get so many forms and if I could help them fill them out and send them remotely this would be worth real money to me.
