Custom fintech software development services · EonTech Poland

Custom fintech software development services,
regulated-grade by default.

EonTech is a Poland-based partner for custom fintech, banking, trading, insurance, mortgage, invoice, and accounting software. Senior EU engineers who have shipped audit-ready financial systems before. One team, one contract, one accountable escalation path — from ledger design to a regulator's walk-through.

Start your project Fintech overview
  • PSD2 · MiFID II · DORA · PCI DSS 4.0
  • Senior EU teams · your time zone
  • GDPR · ISO 27001
Regulated-grade
PSD2, MiFID II, DORA, PCI DSS, and IFRS-aware from day one
Senior only
Financial software engineers who have shipped audit-ready systems
Your IP
Code, models, and data pipelines stay yours

Why this page exists

A working guide to custom financial software development services at EonTech

Financial software is where correctness stops being negotiable. Every debit needs its credit; every order needs its confirmation; every claim needs its evidence; every retention rule needs its audit trail. Off-the-shelf platforms cover the middle 60% of most financial workflows, but the last 40% — the parts that are actually your product — is where custom fintech, banking, trading, insurance, mortgage, invoice, and accounting software actually earns its keep. That last-40% work is what our custom fintech software development services are built for.

EonTech is a Poland-based full-cycle engineering agency: custom software development, web and mobile, cloud/DevOps, QA, and custom AI/ML model development. Our financial-software practice sits inside that broader team — so ledgers, real-time reconciliation, KYC pipelines, and fraud/risk models are shipped by the same senior engineers under one contract, one MSA, and one accountable escalation path. The seams between vendors that eat regulated projects do not exist here because there are no seams to eat.

The rest of this page is a practical brief for CTOs, VPs of Engineering, product leads, and CFOs comparing custom financial software development services against a boxed platform, a legacy in-house team, or an offshore vendor without regulated-software pedigree. Everything below is drawn from actual delivery — no fabricated case studies, no stock statistics, and no promises about regimes we would not certify against.

What we build

Eight shapes of custom financial software we deliver

The financial-software category is not one product. It is eight distinct shapes with eight distinct sets of constraints — and one senior bench that can move between them because the underlying primitives are shared.

  • Custom fintech software development

    End-to-end fintech products — neobank cores, wallets, payments, ledgers, and everything that connects them. The parent shape of our custom fintech software development services.

  • Custom banking software development services

    Core banking extensions, onboarding, KYC/KYB, account and card issuing, and internet-banking front ends built to survive audit and scale past the first million accounts.

  • Custom trading software development services

    Order-management systems, execution paths, low-latency market-data pipelines, back-office post-trade, and MiFID II-aware reporting for brokers, market makers, and prop desks.

  • Custom insurance software development services

    Underwriting workflows, policy admin, claims, and broker portals — with the audit trails and rate-book tooling regulated insurers actually need.

  • Custom mortgage software development services

    Loan-origination systems, servicing platforms, and borrower portals with the document, compliance, and decisioning flows mortgages actually run on.

  • Custom invoice software development services

    E-invoicing, AR/AP automation, PEPPOL and country-specific e-invoicing (KSeF, FatturaPA, Chorus Pro), and reconciliation tooling — with the country compliance matrix built in.

  • Custom accounting software development services

    Ledger, closing, consolidation, and reporting software with IFRS/GAAP awareness and clean integration paths into the ERPs finance teams already run.

  • Custom financial software development services

    The cross-cutting layer: treasury tooling, corporate finance dashboards, FP&A platforms, and the integrations between them. Built for the CFO's desk, not the general-purpose SaaS user.

Key benefits

Why regulated buyers pick a nearshore partner for custom banking software development services

Six practical reasons EU and UK financial-services teams choose EonTech over generic offshore vendors, big-consultancy engagements, or captive vendor lock-in.

  • Regulated-grade from day one

    PSD2, MiFID II, DORA, PCI DSS 4.0, GDPR, IFRS, and country-specific regimes are architecture inputs, not last-week checklists. Financial audits stop being ambush events.

  • Nearshore Poland, EU-native

    Full-day CET overlap for the UK, EU, and Nordics, and half-day for US East Coast. Same GDPR framework as your buyers — DPAs and SCCs sign without third-country transfer questions.

  • Senior engineers who read prospectuses

    The people writing the code have shipped financial software before. They understand order books, ledgers, T+2 settlement, IFRS 9, and DORA operational-resilience testing.

  • One partner for software and AI

    Fraud, risk, and reconciliation ML lives inside the same contract as the product build. No handoff between a fintech vendor and a separate AI vendor with a separate compliance review.

  • Audit-native by design

    Immutable event logs, four-eyes controls, evidence-ready change management, and access reviews that survive an FCA/BaFin/KNF/CSSF walk-through.

  • You own everything

    Every commit, model, pipeline, and piece of documentation is yours from day one. No proprietary middleware, no data-locality trap, no lock-in when the engagement rolls off.

How custom trading software development services actually happen

Five steps from mandate to audit-ready release

Every financial-software engagement runs the same arc. Regulations become architecture inputs; the audit story is written as we build; and the release lane is documented before the first production deploy.

  1. 01

    Regulatory & product discovery

    Two-to-four weeks. We map the target regulations, the customer journey, the data model, and the integration surface. You leave with a written scope and a fixed first milestone.

  2. 02

    Architecture & data model

    Ledger design, event backbone, permissioning model, and compliance boundaries are drawn before features are built. In financial software, the shape of the data model decides how much pain future features will cause.

  3. 03

    Build, test, and evidence

    Senior engineers ship in short cycles with weekly demos. Types, tests, security scans, and evidence collection run in CI. Nothing lands on main without the audit story intact.

  4. 04

    Integrate & harden

    Payment rails, KYC/AML vendors, market-data feeds, credit bureaux, tax platforms, e-invoicing gateways, and the internal ERPs that consume the output. Every integration is contract-tested, not just happy-path tested.

  5. 05

    Launch, observe, and iterate

    Production-grade from the first release, with SLOs, alerting, and a documented incident-response process ready before the auditor asks. Iteration is scoped by real usage, not the roadmap document.

Features built in by default

The engineering primitives every custom financial system needs

The eight primitives below are non-negotiable in any custom financial software development services engagement. If a vendor cannot describe how they handle each one, you are looking at technical risk they have not modelled yet.

  • Event-sourced ledger core. Immutable append-only history so any balance, position, or claim can be reconstructed at a point in time.
  • Idempotent APIs. Retry-safe operations across payments, orders, and postings — the non-negotiable of financial APIs.
  • Double-entry accounting semantics. Every debit finds its credit in the same transaction; no floating imbalances.
  • Real-time reconciliation. Continuous match between your ledger and every external counterparty, not a batch job that surprises you on Monday.
  • Multi-currency, multi-entity. FX booking, intercompany, and consolidation logic built into the ledger, not bolted on later.
  • Strong customer authentication. PSD2 SCA flows, WebAuthn, TOTP, and out-of-band flows across web and mobile.
  • Immutable audit trail. Every state change linked to actor, reason, and evidence — auditable without heroic Excel work.
  • Observability & SRE. Golden signals, SLO-based alerts, and DORA-friendly operational-resilience testing baked in.

Main use cases

Where custom insurance software development services land in practice

Six of the most common product shapes our senior engineers ship. Each has a well-understood arc — from regulatory discovery to audit-ready release — which is why we can commit to a fixed first milestone in days, not months.

  • Neobanks & digital banking

    Core banking extension, onboarding, cards, business accounts, and a mobile app that actually meets FCA/BaFin/KNF expectations.

  • Brokers, exchanges & market makers

    Order-management, market-data ingestion, execution routing, and MiFID II transaction reporting under load.

  • Lenders & mortgage originators

    Loan origination, decisioning, servicing, and borrower portals with the document workflow real mortgages need.

  • Insurers & MGAs

    Rating engines, underwriting workflows, policy admin, and claims — with the broker and audit surfaces that keep the regulator calm.

  • CFO offices & finance functions

    Treasury dashboards, FP&A tools, consolidation engines, and the integrations that make month-end close a normal Tuesday.

  • PSPs & payment orchestrators

    Acquirer connectors, routing/cascading engines, chargeback workflows, and reconciliation across dozens of counterparties.

Industry relevance

Financial-services sub-sectors our custom mortgage software development services already speak

Domain fluency shortens every design decision. These are the buyer shapes our senior engineers already know — retail banks, capital-markets desks, insurers, lenders, corporate CFO offices, and asset managers.

  • Retail & business banking

    Personal accounts, SME cash management, cards, and the compliance backbone underneath it all.

  • Capital markets & trading

    Sell-side and buy-side platforms, prop trading, and the low-latency middleware that keeps them honest.

  • Insurance & reinsurance

    P&C, life, health, and specialty lines with rating, policy, and claims workflows tuned to real books of business.

  • Lending & credit

    Consumer loans, SME credit, BNPL, and mortgages with proper decisioning, servicing, and collections.

  • Corporate finance & accounting

    ERP-adjacent finance tooling, closing/consolidation, FP&A, and the compliance-ready AR/AP that finance teams live in.

  • Wealth, asset & fund management

    Portfolio, order, and post-trade platforms for wealth managers, asset managers, and administrators.

Trust & compliance signals

The regulatory posture custom invoice software development services actually require

Financial software lives inside a wider compliance envelope: PSD2, MiFID II, DORA, PCI DSS 4.0, GDPR, ISO 27001, IFRS, and country-specific regimes such as KSeF in Poland, FatturaPA in Italy, or the FCA's rulebook in the UK. Our delivery is built around these standards from the first sprint — never as a pre-launch scramble.

As an EU-based partner we sign standard DPAs and SCCs, run access reviews on your cadence, and hand over the audit evidence your compliance and internal-audit teams actually ask for. DORA operational-resilience testing is planned into the engagement, not bolted on after go-live.

Common questions

What financial-services teams ask about custom accounting software development services

  • What do your custom fintech software development services actually cover?

    Everything from a neobank core to a broker's order-management system to a mortgage origination platform. Our custom fintech software development services span design, build, integration, compliance evidence, and post-launch operations under one senior team.

  • How are custom banking software development services different from a generic core banking implementation?

    A core banking vendor sells a boxed platform. Custom banking software development services fill the gap between that box and your product — onboarding, KYC, account, card issuing, business logic, and the customer-facing surfaces. Where a vendor solution works, we say so; we do not rebuild what already works.

  • Do your custom trading software development services handle low-latency use cases?

    Yes. Our custom trading software development services span order-management systems, market-data ingestion, execution routing, and post-trade back-office. We are honest about where microsecond-scale requirements need FPGA/C++ specialists — we field TypeScript, Java, Go, Python, and .NET; ultra-low-latency FPGA work is not our core.

  • What is included in custom insurance software development services?

    Rating engines, underwriting workflows, policy administration, claims, broker portals, and the audit trails around all of them. Our custom insurance software development services can plug into your policy admin platform of choice or replace a legacy one, staged so the book keeps running.

  • Can you deliver custom mortgage software development services under UK/EU rules?

    Yes. Custom mortgage software development services from EonTech cover loan origination, decisioning, servicing, and borrower portals under FCA (UK), BaFin (Germany), KNF (Poland), and other EU regimes. Document workflows, KYC, credit-bureau integration, and affordability checks are standard.

  • What are custom finance software development services and how are they different from fintech?

    Custom finance software development services usually refer to the finance-function side — treasury, FP&A, consolidation, and the CFO's tooling — while fintech more often describes customer-facing financial products. We build both, and the same senior engineers can move between them because the underlying primitives (ledgers, entities, currencies, audit) are shared.

  • Do your custom invoice software development services handle EU e-invoicing mandates?

    Yes. Our custom invoice software development services cover PEPPOL, KSeF (Poland), FatturaPA (Italy), Chorus Pro (France), and the ViDA changes coming to VAT-in-the-digital-age reporting across the EU. Country compliance matrices are treated as living data, not one-off code paths.

  • What do custom accounting software development services usually include?

    General ledger, sub-ledgers, closing and consolidation, IFRS/GAAP-aware reporting, and clean integration into the ERPs finance teams already run. Custom accounting software development services from EonTech tend to be extensions or replacements of specific painful pieces rather than green-field ERP rewrites.

  • How do custom financial software development services stay compliant with DORA?

    DORA is designed around operational resilience, ICT risk management, and third-party oversight. Our custom financial software development services build DORA thinking in: incident classification, resilience testing, documented recovery objectives, and evidence collection that survives a regulator's read-through.

  • How do you handle security across custom fintech, banking, and trading builds?

    PCI DSS 4.0 scope minimisation, SCA-compliant authentication, threat modelling per feature, dependency and secret scanning in CI, penetration testing per release, and continuous access reviews. Nothing lands on production without the security story documented.

  • What team shapes do you offer for a custom financial software engagement?

    Full-project outsourcing, dedicated pods (engineers + QA + DevOps + a lead), staff augmentation with individual senior engineers, or a scoped consulting sprint. Monthly rolling contracts, no long lock-in, no captive-vendor relationships.

  • Why nearshore Poland for custom financial and fintech software?

    Poland is inside the same GDPR framework as EU and UK buyers, offers full-day CET overlap, and gives senior EU engineering rates that beat both offshore and onshore-agency pricing once financial-grade quality is factored in. For DORA-compliant delivery specifically, an EU delivery centre removes several third-party-risk questions before they are asked.

Related practices

Nearby capabilities at EonTech

Build financial software the auditor calls boring

Tell us the product shape, the target regime, and the counterparties it must reach. We will scope a fixed first milestone in days, then start shipping regulated-grade, audit-ready software.

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