Ask HN: what product to build when NO FEE is available to transfer money.

If you could transfer money with no fee at all, what service or product would you build?

Creditcard has around 2% of fee, paypal 6%, Bitcoin around 0.0001 BTC, and so on.....

What if it NO FEE is needed, which product could we build on top of it?

IOTA, the new altcoin, does that. Just wondering what we can build on top of it.