# Nelo

> Accept payments on the phone you already own. Money lands in your own currency, in your own bank. And it keeps working when the network doesn't.

- [Introduction](https://nelo.udokaam.dev/introduction.md): A payment terminal with no terminal — built for merchants who lose sales when the network goes down.
- [Quickstart](https://nelo.udokaam.dev/quickstart.md): Clone the repo, install the toolchain, and get the test suites green.
- [Architecture](https://nelo.udokaam.dev/architecture.md): Every moving part, what it is responsible for, and where the boundaries are.
- [The trust model](https://nelo.udokaam.dev/concepts/trust-model.md): Why there is no trusted server in the value path, and what the secure element actually proves.
- [Voucher format](https://nelo.udokaam.dev/concepts/voucher-format.md): 202 bytes, version 1 — the wire contract between the phone and the chain.
- [Replay and double-spend](https://nelo.udokaam.dev/concepts/replay-and-double-spend.md): A 128-slot sliding window, why a single counter is wrong, and what the conflict freeze does and does not catch.
- [The Trust Stake](https://nelo.udokaam.dev/concepts/trust-stake.md): The offline limit is bought, not fixed — sublinearly, under a hard cap, revalued at redemption.
- [Vault program](https://nelo.udokaam.dev/reference/vault-program.md): Accounts, instructions and errors for nelo_vault.
- [Packages](https://nelo.udokaam.dev/reference/packages.md): The six TypeScript packages — what each owns, and why it exists outside the app.
- [Services](https://nelo.udokaam.dev/reference/services.md): The double-entry ledger behind the payout leg, and the relay that isn't built yet.
- [Apps](https://nelo.udokaam.dev/reference/apps.md): The merchant till and the payer app — both Expo, both Android.
- [The reserve model](https://nelo.udokaam.dev/economics/reserve-model.md): What the offline guarantee costs, what the insurance line has to be, and what the SKR premium can honestly be priced at.
- [Unit economics](https://nelo.udokaam.dev/economics/unit-economics.md): Four revenue lines, a thin take rate, and the one number the reserve model contradicts.
- [Deployment](https://nelo.udokaam.dev/operations/deployment.md): Devnet, the program keypair, and what has to happen before the next redeploy.
- [Testing](https://nelo.udokaam.dev/operations/testing.md): What is proven, what is written but unexecuted, and what the gap has already cost.
- [Project status](https://nelo.udokaam.dev/operations/status.md): What is built, what is proven, what is stubbed, and what is not started.