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Core and near-core systems

Custom Banking Software Development for Banks and BaaS Providers

As a banking software development company, we build ledgers, product engines, payment hubs and integration layers around a bank's core, from the team behind FastPost, a ledger that processes a billion transactions in under an hour.

Book a scoping callBanking and fintech engineering

Banking systems we built, measured in production

1,000,000,000
financial transactions in under an hour on an in-memory ledgerFastPost, developed for Legerity from 2013
Sub-second
queries over billions of balancesFastPost production figure
Nearly 10 years
our engagement with Legerity, from 2013Nathan Pesin, CTO, Legerity Financials
Who it is for
Banks, banking-as-a-service providers and fintechs moving to a banking license
What we build
Ledgers, product engines, payment hubs, integration layers, KYC and reporting
How it is sold
Modernization sprints, time and materials builds, managed support or team extension
Constraints we work to
Your change management and access controls, DORA evidence, and a parallel run before cutover
Goals

The modern banking problems we solve around the core

New products, a legacy core and regulators who want evidence, all at the same time.

  • Ship products without a core release

    Deposit, lending and fee products defined as configuration and launched while the core stays as it is.

  • Retire the core one module at a time

    New channels and products on the new side of a strangler seam, with the old core shrinking module by module over the years.

  • Pass third-party risk review quickly

    A short supplier chain, EU-based engineers, your access controls and a documented exit plan.

  • One ledger every report agrees with

    Regulatory and management figures drawn from a single versioned ledger.

  • The bespoke metal exchange platform works great, it is easily accessible and richly functional. Stratoflow managed deadlines capably, meticulously documented their progress, and delivered a complex project at an affordable cost.
    Bartłomiej KnichnickiVice Chairman, Supervisory Board, Mennica Skarbowa
What we build

Banking software development: what we build

  • Ledgers

    General and sub-ledgers as versioned facts with sub-second balance queries, the model behind FastPost for Legerity.

  • Product and pricing engines

    Deposit, lending and fee products defined as configuration, priced by rules you can read, launched without a release.

  • Payment hubs

    Instant, batch and card rails behind one integration layer, with idempotency and reconciliation designed in.

  • Onboarding and KYC orchestration

    Workflow across identity, screening and document providers, with the decision trail regulators ask for.

  • Integration layers

    The strangler seam around a legacy core: the layer that lets new channels and products ship while the core stays as it is.

    Application modernization

  • Reporting and reconciliation

    Regulatory and management reporting that reconciles to the ledger, with day-end runs that finish inside their window.

    Performance engineering

  • Lending platforms

    Origination, decisioning, servicing and collections platforms with a versioned ledger underneath, built around your products.

    Lending software development

  • Mobile banking back ends

    The APIs, security and services behind a mobile banking app, for the client your team or a partner builds.

    Mobile banking app development

Case studies

Banking-grade systems we built

All case studies

How we help

Services for banking systems

Questions we get asked

Questions about custom banking software

Do you replace core banking systems?

Rarely all at once, and we will argue against doing that. The approach that works is a strangler seam around the core, with new products and channels on the new side and the core retired module by module over years. We deliver that in scoped phases, and the first phase sets the ballpark for the rest.

How do you meet a bank's third-party risk requirements?

Direct employees only, EU based, your access controls and change management, DORA-style incident and continuity evidence, and a documented exit plan in every contract.

How much does custom banking software cost?

A written ballpark per component or module set after the scoping call, a monthly retainer for support, or a monthly team fee. Every number is given in writing, and the first delivery phase shows in working software what the rest is likely to take.

Will the bank own what you build?

Yes. The code sits in repositories you control from day one, the agreement assigns ownership to you, and handover with documentation is part of the scope.

How big is the team behind it?

A boutique team of senior engineers, every one a direct employee. In a bank’s third-party review that means a short supplier chain and a named team.

What technology sits behind a custom banking system?

Java and Spring for the services, an in-memory data grid where balance queries have to stay sub-second, Kafka for events between the core and new channels, and PostgreSQL as the relational store.

What should we look for in a banking software development company?

Systems it has run with money in them, and the names of the people who built them. Ask how the company works within your change management and access controls, what evidence it produces for a DORA third-party review, and what the exit plan in the contract says. Our reference is FastPost, the ledger we developed for Legerity over nearly ten years.

Go deeper

Banking guides from our engineers

All articles

Written by , Co-founder and CEO, Stratoflow. Published . Updated .

Next step

Schedule a scoping call about your banking system

Thirty minutes with an engineer on the system around your core, what has to change and by when. You leave with a written view of scope and price model.

Book a scoping callBanking and fintech engineering