Fintech Software Development Services for Banks and Fintechs
Ledgers, pricing engines, payment and lending platforms in Java and Spring, from the team that built FastPost, a ledger that processes a billion financial transactions in under an hour. We work to the resilience rules DORA sets for banks and their technology suppliers, and you get a written ballpark after the scoping call.
Finance systems we built, and the rules they run under
- 1,000,000,000
- financial transactions in under one hour, in-memory ledger and reportingFastPost, developed for Legerity from 2013
- Nearly 10 years
- our first finance engagement, with Legerity from 2013Nathan Pesin, CTO, Legerity Financials
- Jan 2025
- DORA applies to EU financial entities and sets requirements for their ICT suppliersRegulation (EU) 2022/2554
Financial services clients and partners
What every bank and fintech wants from a fintech software development company
Whether the client is a bank or a fintech, the same four goals come up: faster launches, a close that finishes on time, evidence for regulators and AI an auditor can follow.
Launch products without waiting for the core
New deposit, lending and fee products defined as configuration and launched in weeks, while the core keeps running.
A close that finishes every day
Day-end and month-end processing that finishes inside its window, so finance works from today’s numbers.
DORA evidence from the engineering itself
Continuity tests, incident runbooks and third-party evidence produced as part of delivery.
AI features an auditor can follow
Retrieval and agent tooling with the logging, human approval steps and documentation a financial regulator expects.
Common problems in banking and fintech systems and how our engineers fix them
Four problems we see most in banking and fintech systems, each with a service built to fix it.
The batch that does not finish
Day-end and month-end runs that outgrew their window. In-memory processing and partitioning took one client's ledger to a billion transactions in under an hour.
A Java 8 core that is risky to change
Java 8 systems that run the bank, modernized a few modules at a time behind a strangler seam, with the old system running until the new one is trusted.
Resilience you have to evidence
DORA asks for tested continuity, incident reporting and third-party risk management. We build the runbooks, tests and evidence as part of the engineering work.
AI features that have to pass an audit
Retrieval over transaction and document data and agent tooling for operations teams, with the audit trail and human approvals a financial regulator expects.
Finance systems we built
- Flagship · Banking and fintech · from 2013
FastPost: a billion financial transactions in under an hour
FastPost, a rule-driven, high-performance accounting platform developed for Legerity by Stratoflow from 2013, used by telcos and insurers worldwide.
1,000,000,000 transactions / hour
- Ecommerce · Banking and fintech
Mennica Skarbowa: real-time pricing engine for an omnichannel precious-metals platform
Intraday base prices from London Metal Exchange and distributor feeds, a rules-driven margin engine, and price distribution to web stores and physical shops.
Intraday repricing, every channel
- Banking and fintech · Integration
Kusiri: forensic data platform integrations, later acquired by PwC
Third-party data integrations and performance tuning on an OSGi-based Java platform for due diligence and anti-money-laundering search.
Acquired by PwC
Banking and fintech systems we build
Lending software development
Origination, decisioning, servicing and collections platforms with a versioned ledger underneath.
Mobile banking app development
The back end, APIs and security behind a mobile banking app. Your team or a mobile partner builds the client; we build what it calls.
Custom banking software development
Core and near-core systems for banks and banking-as-a-service providers: ledgers, product engines, integration layers.
The developed software product was built from scratch with solid quality. We have had a long-term engagement with Stratoflow for nearly 10 years. We look at them as partners, rather than contractors. I'm impressed by their team culture and cross-team support.
Services for banks and fintechs
Dates that shape banking and fintech engineering
EU rules on resilience, payments and AI set deadlines for banks, fintechs and their software suppliers. Each one changes what the systems must do, so we design for it early.
- Jan 2025
DORA applies
For EU financial entities, and through their contracts their ICT providers: incident reporting, tested continuity, exit plans and register entries. We produce the evidence as part of the engineering.
- 2025 to 2027
Instant payments
Euro-area providers first, others from 2027. Ten-second settlement leaves no time for a retry loop, which changes how payment integrations are designed.
- In negotiation
PSD3 and the PSR
Tighter open-banking access, fraud liability and strong customer authentication. We design payment and API layers so these changes can be made through configuration.
- Dec 2027
AI Act high-risk rules
Creditworthiness assessment and some pricing become high-risk uses. Any model in a lending or pricing path is built with that documentation in mind.
When a packaged product is the better answer
If your products are conventional and your volumes modest, a packaged core, a lending product or a banking-as-a-service provider will cost less than a build, and we will say so on the scoping call. A fintech software development company like ours is worth talking to when volume, product rules or integrations have made the packaged answer the constraint.
Questions about fintech software development
Do you work with regulated financial institutions?
Yes, including banks. That means working to your existing audit, access control and change management requirements, providing the DORA third-party evidence your compliance team needs, and accepting that some decisions are not ours to make quickly.
How much does fintech software development cost?
It depends on the offer. A Modernization Sprint or Performance Rescue gets a written ballpark after the scoping call and is billed time and materials; Team Extension is a monthly fee per engineer; Managed Support is a monthly retainer. For a new platform, the written ballpark after the scoping call gives you the range before you commit. Every figure is given in writing.
How do you approach performance work on an existing financial system?
We measure before changing anything. In the finance systems we have worked on, the cause was usually a few queries, a serialization point, or work done per transaction that could be done once. Performance Rescue is built for this, with SLO targets in the proposal.
Can you take over a system another vendor built?
Yes. The first step is the scoping call and a written ballpark, including if the honest answer is that a rewrite costs less than the repair.
Are you big enough for a bank?
We are a boutique team of senior engineers, all direct employees, with no subcontracting. The people you meet on the scoping call write the code. That keeps third-party risk reviews short, and every contract carries a documented exit plan.
Will we be locked in to Stratoflow?
No. Work takes place in repositories you control, the agreement assigns ownership of the delivered work to you, and handover with documentation and knowledge transfer is part of the scope.
What technology do you use for banking systems?
Java and the JVM for the systems that carry load, with Spring Boot, in-memory data grids (Hazelcast, Oracle Coherence, Apache Ignite), Kafka and PostgreSQL where they fit, and Spring AI for model integration. We keep to the stack banks already run and can audit.
Where are you based and how does that affect a UK or US bank?
Poland, inside the EU and one hour ahead of London (CET): we work UK business hours in full and overlap the US East Coast every morning. All engineers are direct employees, which simplifies the third-party risk paperwork.
Banking and fintech guides from our engineers
- Fintech and Banking
Fintech Trends 2026: AI Results, Profitable Growth and Instant Payments
The fintech trends that matter in 2026, with current data: investment returns for fewer and larger companies, AI that works in fraud and fails without a human route, instant payments, open banking rules, embedded finance after Synapse and APP fraud reimbursement.
- Fintech and Banking
Banking Technology Trends 2026: 8 Shifts That Matter for Bank Leaders
Eight banking technology trends for 2026, backed by data: mobile banking as the main channel, core banking modernization, AI with measured returns, instant payments, scams, DORA and fintech partners.
- Fintech and Banking
Payment Integration: How Payment Gateways Work, Explained
How payment gateways work step by step, the integration options, PCI DSS and how to build a reliable integration.
Book a scoping call about a financial system
Bring the system and the number that has to change: throughput, close time, cost per transaction, or a regulator's deadline.