Rotating savings circles (hui, arisan, tanda, chit funds) as smart contracts: collateral and a winner's bond instead of trust, discount auctions, and a portable on-chain savings record.
Over a billion people save in rotating savings circles: hui in China, arisan in Indonesia, tanda in Mexico, susu in Ghana, chit funds in India. A group agrees on an amount, everyone pays in each round, and each round one member takes the whole pot. It runs on trust, and it fails the same way everywhere: someone takes the pot early and stops paying.
Potluck puts the circle in a smart contract on Arbitrum, paid in USDG, with no organizer in the middle.
• Collateral instead of trust: every member locks a small collateral. A missed payment is covered from it automatically, so the pot is always whole.
• Winner's bond: whoever takes the pot early has part of it held back (capped at what they still owe) and gets it back when the circle ends.
• Auction mode: members who need money now bid a discount to take this round's pot, and the discount is shared by everyone who waits. It is how a Chinese hui or an Indian chit fund prices money, without the organizer.
• Portable savings record: when a circle completes, each member's on-time payments, missed payments and defaults are written to PotluckReputation, an open on-chain registry any lender or protocol can read.
• No admin keys, pull payments: settlement only credits balances and each member claims their own money, so one frozen or broken address (USDG can freeze addresses) can never lock the circle for everyone else.
Try it alone in three minutes: the 'Try it alone' page adds two bot members that live in your browser tab. They join, pay, bid and settle on their own, so one judge can play a whole auction circle on the testnet.
Evidence: 15 unit and fuzz tests plus 3 invariant tests (15,000+ random calls checking the circle always holds exactly what it owes), a frozen-member test, Slither review in SECURITY.md, CI on every push, and verified contracts.
Live on Robinhood Chain Testnet (an Arbitrum Orbit chain). App: https://luoy16002-svg.github.io/potluck/ · Try it: https://luoy16002-svg.github.io/potluck/#/practice · Code: https://github.com/luoy16002-svg/potluck
Everything was built during the buildathon:
• Contracts: PotluckCircle, PotluckFactory, PotluckReputation and a 6-decimal test USDG with a faucet.
• Tests: 15 unit and fuzz tests (including a money-conservation fuzz test and a frozen-member test) plus an invariant suite; Slither reviewed; GitHub Actions CI.
• React + viem frontend with no backend: create, join, pay, bid, settle, claim, withdraw, look up any address's savings score, and a 'Try it alone' mode with in-browser bot members.
• Deployed and verified on Robinhood Chain Testnet, with completed demo circles (fixed order and auction with a bid every round) and many practice circles run end to end.
• Security iteration: v1 paid winners directly; v2 switched to pull payments so a frozen address cannot block settlement.
• Pitch and demo videos with a live on-chain walkthrough.
Not raised. Bootstrapped solo project, open to grants and ecosystem support to launch on Arbitrum One and Robinhood Chain with native USDG.