Systems we build

Payments, wallets & ledgers

The money layer of your product, built to be auditable from day one — Stripe payments with per-country VAT, multi-currency wallets on an append-only ledger, usage-based and subscription billing, and webhook-driven flows that survive retries without ever double-charging anyone.

30 min with a full-stack devAll services

Proof, not promises

Payments, wallets & ledgers we've shipped

Covo — An eSIM wallet for international travelers
Fintech · Travel / eSIM
Covo

The backend and mobile apps behind a travel eSIM wallet — an append-only multi-currency ledger, family pooling, instant top-ups.

How we think, not just what we type

Concepts & patterns we work in

The ideas behind the tools — the patterns we've applied in production, not buzzwords.

Append-only, reconcilable ledgersStore in one currency, display in the user'sIdempotent, webhook-driven billingPer-country VAT computationUsage metering & cost observabilityWallet pooling & spending capsAudit trails

Languages, frameworks, infra

What we actually use

The tools and languages we have real, shipped experience in — not a wish list.

Payments
StripeApple Pay / Google PaySaved methods & auto-refill
Ledger
Append-only ledgerMulti-currency display (135+)Reconciliation
Billing
Usage-based / pay-as-you-goPer-country VATBonuses & gifting
Core
Open Mercato

Explore further

Custom ERP & business systems →Booking & reservation systems →

Bring the napkin sketch.

Thirty minutes with a full-stack engineer, plus a short written report that's yours to keep.

30 min with a full-stack devSee services →

30 minGoogle Calendarno sales deck

Prefer to write? Send us a message →