UBIC is a blockchain where people receive coins every block once they have scanned the NFC chip contained within their passport.
Every country has it's own currency, so there has already been quite a lot of OTC trading between the currencies of each countries.
In the white paper it was proposed to do those onchain, and it seems easy to implement:
https://github.com/UBIC-repo/Whitepaper#onchain-currency-exchangeIs some one interested in building some thing like that?