Nebula — Core Banking Modernisation
Replacing a twenty-year-old mainframe ledger with an event-sourced core, without a single hour of customer downtime.
What was actually broken.
A mid-sized digital bank was running its ledger on a mainframe core that could only close books overnight, could not express new product types without a vendor change request, and cost more each year to keep certified. Every roadmap conversation ended at the same wall. Replacing it outright was unthinkable — the ledger is the bank.
How we went at it.
We ran a strangler-fig migration. A new event-sourced ledger was built alongside the mainframe and fed the same transaction stream, running in shadow mode for five months while we reconciled every balance to the cent, daily. Once shadow reconciliation held at 100% for sixty consecutive days, product lines were cut over one at a time — savings first, then current accounts, then lending — each behind a feature flag with a tested rollback path.
Where it landed.
The mainframe was decommissioned fourteen months after kickoff. Balances now settle continuously rather than overnight, and the product team ships new account types in days using a configuration model rather than a vendor ticket.
The shadow-running period was what sold our board. We watched the new ledger agree with the old one every single day for five months before anyone touched production.
Helix — Clinical Coordination Platform
Let's build the thing that moves your numbers.
Tell us what is actually blocking you. Forty-five minutes, no deck, no obligation — and a straight answer about whether we are the right team for it.