In 2011 at a hackathon I built rsvp.io (now points to a silly game of mine) to allow wedding couples to easily create a custom wedding invitation rsvp page. A unique code could be added to a paper invite, or the page used on its own. After the hackathon I spent another month or so refining the site. I never took it far enough, but might have made a little money had I tried. Some ideas that I never took forward were partnering with printing agencies for paper invites, and affiliate income for gift registry.

It did get used once however, for my wedding in 2013 :)