Blnk

Blnk is a ledger for teams building financial products such as wallets, payment platforms, and lending apps. It records every money movement as a double-entry transaction, so balances stay accurate from the first transaction to the hundred-millionth.

Records are immutable. Nothing gets edited or deleted, history is only appended. Concurrent transactions are ordered and applied safely, so heavy traffic doesn't corrupt balances.

• Multi-currency: hold fiat, points, and crypto in one ledger, tracked to the smallest unit.
• Inflight transactions: hold funds, then commit or void once checks like fraud, KYC, or sanctions clear.
• Split transactions: record fees, spread revenue, and disbursements in a single request.
• Overdrafts: let balances go negative within set limits.
• Bulk transactions: process large batches, with optional all-or-nothing commits.
• Fund lineage: see what share of a balance came from each source.
• Reconciliation: match ledger entries against external records and flag discrepancies.

You post transactions through a REST API or SDKs for TypeScript, Go, Python, and Java, and the ledger can sit in front of any payment provider or rail you already use.

You can self-host it, or run it on Blnk Cloud, a managed option with dedicated infrastructure, backups, high availability, and a 99.9% uptime SLA. Paid Pro Support adds a private Slack channel, ledger design help, and migration from in-house ledgers. Blnk is ISO/IEC 27001-certified and GDPR-compliant, with encryption at rest and in transit and role-based access control.

If you're weighing ledger APIs, Fragment and Twisp are comparable options.