Inspiration
I wanted to bring prediction markets to small groups: friends, clubs, and communities. Existing tools are either too broad (global markets) or too informal (group chats and spreadsheets). I was inspired by the idea of private prediction markets: lightweight, still trustworthy, and fun for groups to bet on shared questions like “Will our demo work?” or “Will John go on a 2nd date?” I also wanted to explore how Solana could provide a transparent, immutable record of trades without forcing users to manage wallets or crypto directly.
What it does
MicroMarkets is a cross-platform app (iOS, Android, web) for private prediction markets inside groups. Users:
- Create or join groups with a 6-character code and a base buy-in (e.g. $10)
- Create markets on any yes/no question, set initial odds, and add liquidity
- Trade by buying YES or NO shares; prices move with the pool
- Resolve markets (creator only); winners split the total pool proportionally
- View leaderboards and past markets per group
Trades are recorded on Solana Devnet via a custom Anchor program, so activity is verifiable and tamper-resistant. Groups and balances live off-chain for speed and simplicity, while the ledger provides a permanent audit trail.
How we built it
Frontend: Expo (React Native) with file-based routing, shared across iOS, Android, and web State: In-memory store with AsyncStorage persistence for groups, markets, and balances Solana: Custom Anchor program in Rust that records trades as PDAs (market ID, user, nonce) Ledger server: Node/Express server that signs and submits trade transactions to Solana Devnet
Challenges we ran into
Hybrid architecture: Deciding what to put on-chain vs off-chain. I kept groups and balances off-chain for UX and cost, and used Solana only for trade records. Solana PDAs: Designing PDA seeds for trade accounts (market ID, user, nonce) so each trade has a unique account and avoiding seed collisions. Ledger server auth: The server signs for all trades, so I had to design around trust and key management. I'm currently using a single server keypair; production would need per-user or delegated signing.
Accomplishments that we're proud of
End-to-end flow: From group creation to market resolution, smooth UX. Market mechanics: Odds derived from pool sizes, with proportional payouts on resolution On-chain transparency: Every trade is recorded on Solana, so groups can verify activity
What we learned
Anchor and Solana PDAs are powerful for building verifiable, append-only ledgers Hybrid designs (off-chain state + on-chain proofs) can balance UX and trust Parimutuel markets are easier to implement than order books and work well for small groups. Market making is unrealistic here.
What's next for MicroMarkets
Build a full authentication system and publish!
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