Sending bitcoin to somebody immediately next to you is still a hassle. QR codes are cumbersome, most of phones still don't support NFC and trying to copy the address manually is very error prone. But 100% of phones have reproductor and microphone, so why don't use that :)
What it does
Uses sound to send bitcoin between two phones.
How we built it
We used chirp.io SDK to encode data in audio, Coinbase API to simplify work with bitcoin and Swift and Java to build applications for both major platforms.
Challenges we ran into
Very uneasy implementation of the Coinbase API and Oauth 2 authentification flow. Luckily we are skilled debuggers, so it didn't take too long :)
Accomplishments that we're proud of
Very fast data exchange and user experience that feels similar to being in Star Wars (beeping during transaction sounds almost like R2-D2 :D).
What we learned
How tough it is to send p2p data between iOS and Android. Proper way to implement Oauth 2 both on iOS and Android.
What's next for Chirpcoin