OpenTab

Inspiration

A family can send money abroad in seconds, yet their loved one may still have to travel to collect cash and pay to convert it before buying groceries. We wanted families to be able to spend that money directly at a local shop.

What it does

OpenTab lets families fund a shared spending vault for loved ones abroad. At checkout, the shopper scans the shop’s QR code, reviews the amount, and approves the bill offline. The merchant scans that approval and gets paid online through Stellar in seconds with low network fees.

How we built it

We connected our web app to a Soroban smart contract on Stellar Testnet. When the merchant submits a signed approval, the contract checks the signature and vault balance, then pays the merchant using OTUSD, our demo token.

Challenges we ran into

An offline phone can approve a bill, but it can’t confirm the vault’s current balance. We built that check into the contract and made each approval usable only once, so retrying a payment can’t charge the family twice.

Accomplishments that we're proud of

We completed a Testnet purchase with the shopper’s phone in airplane mode and verified the merchant’s payment on Stellar. We also tested the app with three family members.

What we learned

Shoppers need to know which shop and amount they’re approving. Merchants need to know when the money has arrived. Showing those moments separately keeps checkout clear, even for someone who’s never used crypto.

What's next for Opentab.

Next, we’ll test the full checkout on two physical phones and pilot it with families and local shops to see whether it saves a trip to collect cash. We also plan to add USDC support and explore local-currency payouts for merchants.