I've been working on an iOS app called snapmail: lets you take any photo on your phone, filter / sticker it, and send it as a 4x6 postcard anywhere in the U.S. for $2.99. Fun way to stay in touch with friends & fam. One of a few no-account-needed, single use iOS apps I've been working on.
TestFlight for now - try it out here: https://testflight.apple.com/join/wKY4eYV8