Gatorstar

Inspiration

We're a group of friends who are always planning something: a spring break trip, concert tickets, a big group dinner. The fun part was easy. The money part was so annoying. One person fronts the Airbnb, someone else "will Venmo you later," three group chats argue about who still owes what, and by the time the trip comes around half the group hasn't saved anything.

We asked ourselves: what if saving for a group goal felt as social as planning it? So we built a way to pool money toward a shared goal, track who's actually putting in their share, and make it fun to stay accountable. Then we added our own twist: financial education and a bit of friendly social pressure.

What it does

Gatorstar is a social savings app for friend groups.

Shared group goals. Create a group, invite friends, and set a goal (amount, deadline, how often everyone pays). Every contribution is a real withdrawal from your linked bank account, so your balance updates instantly.
Gemini goal coach. Not sure how to plan it? A guided chat asks what you're saving for, how much, by when, and how often, then checks how realistic the plan is against your own spending and fills in the goal form for you.
Accountability that bites (a little). Groups choose what happens when someone misses a payment: a money penalty (a % added to their share) or an honor-code dare the group enforces, fantasy-football style.
A verifiable vault on Solana. Each goal has its own on-chain vault. Every dollar saved is mirrored as a token on Solana devnet, so anyone can check that the money is really there. The vault works like escrow: it stays locked until the goal is reached, then the organizer releases it in one transparent payout. A "Verify on Solana" button checks every transaction straight from your browser, and a "Try to cheat" demo shows the blockchain catching a tampered record. Share a public proof page with a QR code.
Weekly budgets + points. Set weekly limits per category (or let Gemini propose them from your real spending). Stay under budget to earn points, build streaks, and get Gemini tips on where you could save.
Social. A live activity feed of what your friends are doing (savings, streaks, goals reached), reactions, cheers, and a weekly leaderboard. Privacy first: friends see points and percentages, not your purchases.
Learn. Short money lessons Gemini tailors to your spending, quizzes that earn leaderboard points, and an "Ask Gemini" box for money questions.
Live updates and celebrations. When a friend contributes, your screen updates within seconds. When a goal is hit, everyone gets confetti. 🎉

How we built it

Frontend (Mandy H, John Z): Figma + Vite + TypesScript + deployed on Railway.
Backend (Alwin C, Austin L): Python FastAPI + TypeScript with SQLite
Banking: Capital One's Nessie API as our mock bank (accounts, purchases, deposits, withdrawals).
AI: Google Gemini with structured JSON outputs, in two tiers: a fast, lightweight model for chats and a stronger one for heavier analysis. Every Gemini feature has a time budget and a built-in fallback, so the app never hangs waiting on AI.
Blockchain: Solana devnet using an SPL token (1 token = $1, stored in cents), with a vault wallet per goal and a memo on each transaction tying it to the bank record. We send raw JSON-RPC and sign transactions with solders. A background queue sends and confirms transactions so the bank side never waits on the blockchain.
Points: each week, for every budgeted category with limits and spending streaks, points are calculated using a mathematic equation to determine the amount of points assigned based off of financial lessons, reaching goals for bonuses, spending, and fund contributions.

Challenges we ran into

Nessie's quirks. Balances never change, transfers are rejected, and some transactions can't be deleted. We built our own ledger logic that computes balances from transaction history, and we hide undone transactions.
Slow API calls. Nessie and Gemini can each take seconds. We added parallel fetching, caching, a shared request de-duplicator, model tiers, time budgets, and backup planners so every page stays snappy.
Getting Solana right. Signing SPL token transfers by hand, paying fees from an app wallet, dealing with devnet faucet limits, and keeping the on-chain vault in sync with the bank records, including refunds and escrow release.
Privacy vs. social pressure. Accountability works best when friends can see progress, but nobody wants their purchases broadcast. We settled on points, streaks and percentages, with dollar amounts only inside the groups you share and an opt-in setting for more.
Live updates without a full real-time server: a lightweight change counter that every open app polls, so pages refresh only when something they care about changes.

Accomplishments that we're proud of

A working on-chain escrow vault that anyone can independently verify from their browser, plus a tamper demo that shows why blockchain matters for group money.
Gemini features that feel genuinely helpful: they use your real numbers to fill in forms for you, instead of just chatting.
Turning budgeting into something friends actually want to open: streaks, leaderboards, cheers, and confetti.
It degrades gracefully: if Gemini or Solana is slow or down, the app keeps working and catches up later.

What we learned

How real ledgers work (balances are derived, not stored) and how to design around a limited bank API.
How to use LLMs reliably in a product: structured outputs, validating the model's answers, fast vs. smart models, and always having a fallback.
The basics of Solana: SPL tokens, associated token accounts, transaction signing, confirmations, and how to make on-chain data understandable to non-crypto users.
That the hardest part of group finance isn't the math. It's the social side, and design matters as much as code.

What's next for Gatorstar

Real bank connections and real payments (e.g. Plaid + instant payouts), with escrow release to the booking or vendor directly.
Splitting shared expenses after the trip ("who paid for gas?"), not just saving before it.
Smarter Gemini coaching: mid-goal check-ins, "you're behind, here's a catch-up plan," and personalized lesson paths.
Group-vs-group challenges and seasonal leaderboards.
A mobile app with push notifications for cheers, reactions, and payment reminders.