Software is the nervous system of any bank, lender or fintech. Every loan that is originated, every transfer that settles and every payment that is reconciled depends on platforms that must respond in milliseconds, operate without errors and hold up under demand spikes. In that context, software development for banks and financial institutions is not just another IT project: it is mission-critical infrastructure on which daily operations, regulatory compliance and customer trust directly depend.

At Intway we have been building, integrating and modernizing financial software for more than 25 years. We work with traditional banks that need to modernize a legacy core, fintechs building their platform from scratch, lenders digitizing loan origination, credit unions opening digital channels for their members, and insurance companies integrating their systems with new products. This document explains in detail what we build, how we do it and with which technologies, so that any organization looking for a partner in software development for financial institutions knows exactly what to expect.

Banking, lending and fintech software: one goal, three different realities

Although they are often grouped under the "financial software" label, a bank, a lender and a fintech start from very different situations, and a sound technical strategy has to acknowledge that. A traditional bank's banking software almost always coexists with a legacy core, regulated processes and a very low tolerance for risk. A fintech, by contrast, usually builds on a blank slate, prioritizes time-to-market and needs an architecture ready to scale fast without accumulating technical debt. A lender concentrates value in origination and credit management, while a credit union above all needs simple, reliable digital channels for its members.

Understanding that difference is what allows us to choose the right approach: incremental modernization for the bank, a new modular platform for the fintech, and integration layers when the job is to connect the new with what already works. In every case the common denominator is the same: critical, highly available, secure and auditable software.

What kind of projects do we build?

Software development for the financial sector spans a wide range of modules and products. These are the types of solution we build and integrate most often:

• Core banking and transactional engines.
• Home banking and digital banking for individuals.
• Mobile banking and native financial apps.
• Digital onboarding and fully remote sign-up.
• KYC and identity verification.
• Document management and digital files.
• Loan origination and credit decision engines.
• Personal, secured and mortgage loans.
• Credit and debit cards.
• Checking accounts, savings accounts and time deposits.
• Investments, mutual funds and trading platforms.
• Treasury and liquidity management.
• Back office, operations and internal support.
• Collections and debt recovery.
• Rules engines and configurable financial workflows.
• Digital and electronic signature.
• ERP and accounting system integrations.
• Open Banking APIs and embedded financial services.
• Banking middleware and integration buses.
• B2B portals and channels for merchants and members.

Each of these can be developed from scratch, integrated with existing systems or combined into a larger platform. The decision depends on the institution's starting point and where the greatest business return lies.

Legacy system modernization for banks and lenders

Much of banking still runs on legacy systems: business-critical applications written ten, twenty or even thirty years ago that remain the heart of operations. It is common to find core banking systems in COBOL on AS400 (IBM i), modules in Visual Basic or Delphi, screens built with Oracle Forms or PowerBuilder, and business layers in old versions of Java. Being legacy does not mean being bad: many of these platforms are extraordinarily reliable and have processed millions of operations for decades without failing. The problem arises when maintenance becomes expensive, when adding a new feature takes months, and when the knowledge to operate them depends on fewer and fewer people.

The most common and most costly mistake is trying to replace everything at once with a "big bang" project. Rewriting a full core in a single release means long timelines, high budgets and enormous operational risk: while the new system is built, the old one keeps evolving, and keeping both in sync becomes a problem in itself. The strategy we recommend is incremental modernization: evolving the platform in stages, without stopping operations.

In practice, the approach follows a clear sequence. First we assess the current system to understand its architecture, dependencies and the critical processes it supports. Then we prioritize the modules that generate the most cost, incidents or friction for the business. On those modules we apply the strangler fig pattern: we expose legacy functionality through APIs and banking middleware, so new development consumes services without depending on the internal implementation. From there we build the new components with modern architectures, integrate them progressively and, once they prove stable in production, safely decommission the old components they replace.

The result is a low-risk transition: the institution keeps operating normally, investment is spread over time, results appear in weeks rather than years, and technical debt is steadily reduced. There is no single valid architecture for every case; the right strategy depends on transaction volume, availability requirements and the constraints of the existing system. What remains constant is the guiding principle: modernize without disrupting the business.

Core banking and digital banking development

The core banking system concentrates the fundamental operations: accounts, balances, movements, products and the associated accounting. We work on two complementary fronts. On one side, the modernization of an existing core banking system, exposing it through services and decoupling it from the channels so it stops being a bottleneck. On the other, the development of a new core or satellite modules with service-oriented and microservices architectures, when the institution needs to launch products the legacy core cannot support.

On that foundation we build the digital banking layer: home banking and mobile banking consuming the core APIs, with a modern user experience, low response times and bank-grade security. The key is that channels evolve at their own pace, with frequent releases, without forcing changes to the transactional core on every update.

Banking API development and Open Banking

Banking APIs are the connective tissue of modern banking: they let channels, partners, merchants and third parties consume the institution's services securely and in a controlled way. We design and develop APIs following industry best practices: clear, versioned contracts, REST as the standard (with GraphQL or SOAP where the case calls for it), authentication and authorization with OAuth 2.0 and JWT, an API gateway that centralizes security, throttling and traceability, and end-to-end observability with metrics, logs and distributed traces.

This same approach is what enables Open Banking and embedded finance: securely exposing accounts, payments and information so other products and ecosystems integrate with the institution. Good API design does not only solve the technical integration; it also protects the organization with versioning that avoids breaking consumers, usage limits that preserve stability and auditing of every call.

Integration with existing banking systems

You rarely start from zero. Most financial projects largely consist of system integration: connecting the new with what already works without creating risk. We have experience integrating with core banking systems and in-house engines, COBOL and AS400 platforms, Oracle databases, ERPs such as SAP and Microsoft Dynamics, CRMs such as Salesforce, and systems developed internally by the institution itself.

To achieve this we use the most appropriate mechanism in each case: SOAP web services and REST APIs, queues and messaging with RabbitMQ or Kafka for asynchronous, high-volume integrations, files and batch processes when the source system requires it, and a layer of banking middleware that orchestrates, transforms and decouples. The goal is always the same: systems that talk to each other reliably, with retries, idempotency and traceability, so that an integration error never turns into a lost or duplicated operation.

Payment integration and digital wallets

Payments are one of the most sensitive areas of a financial platform: any failure translates into money. We integrate with processors and acquirers, payment gateways, credit and debit card networks, POS terminals, digital wallets, QR payments, instant transfers and direct debit.

Beyond connecting, we build the mechanisms that make the system reliable at scale: automatic reconciliation between what was processed and what actually settled, controlled retries on transient failures, idempotency handling to avoid duplicate charges and full traceability of every movement. That work, often invisible to the end user, is exactly what separates an integration that "works in the demo" from one that sustains the processing of thousands of transactions per minute.

Security, compliance and high availability

In a financial application, security is not just another feature: it is a cross-cutting requirement designed in from day one and not patched on afterwards. We work with encryption in transit and at rest, strong and multi-factor authentication, granular authorization by role and permission, logs and auditing of every sensitive operation, and traceability that reconstructs who did what and when.

On top of that security foundation comes the demand for continuity. Highly available software is built with failure in mind: redundancy, verified backups, disaster recovery plans, permanent monitoring and alerts that catch a problem before the customer notices. We design platforms to degrade gracefully, recover quickly and provide real-time operational visibility. In a business where an hour of downtime has a direct and reputational cost, availability is part of the product, not an extra.

Technologies and architecture

We choose technology based on the problem, not the trend. Our usual stack for financial projects includes:

• Backend: Java, Spring Boot, Node.js, NestJS, .NET and Python.
• Frontend: React, Angular and Next.js.
• Mobile: React Native and Flutter.
• Databases: SQL Server, PostgreSQL, Oracle and MySQL.
• Cloud: AWS, Azure and Google Cloud.
• DevOps: Docker, Kubernetes and CI/CD.
• Integrations: REST, SOAP, GraphQL, RabbitMQ and Kafka.

In architecture we combine what fits each case: microservices when scale and deployment independence justify them, event-driven architectures for asynchronous, high-volume processing, and simpler, more monolithic designs when they add more value than complexity. We prioritize maintainability, scalability and observability over sophistication for its own sake.

Use cases

The same principles apply to very different realities. These are typical scenarios:

• Traditional bank: modernizing a legacy core by exposing it with APIs, without replacing it all at once, to launch digital products on a stable base.
• Fintech: building a platform from scratch, modular and scalable, ready to grow without accumulating technical debt.
• Lender: digitizing loan origination, with remote onboarding, a decision engine and collections management.
• Credit union: a portal and digital channels for members, simple and reliable, integrated with existing management systems.
• Insurance company: integrating the existing platform with new products, sales channels and payment methods.

Benefits of working with a specialized software factory

Choosing a partner with specific experience in the financial sector changes the outcome. The concrete benefits we pursue in every project are measurable: reduced development and go-live times, automation of processes that are manual today, scalability to grow without rebuilding the platform, high availability to sustain operations, maintainability that lowers the cost of evolution, reduced technical debt and real integration between systems that used to live in isolation. It is not about technology for its own sake, but about turning every technical decision into business impact.

Why Intway

We are a software factory with more than 25 years building enterprise and mission-critical solutions. What we bring to a financial project:

• More than 25 years building enterprise software.
• More than 500 projects delivered.
• Real experience in mission-critical software and high availability.
• Senior teams that integrate with the client's teams.
• Scalable architecture and custom development.
• Integration with existing systems, including legacy environments.
• Quality methodologies aligned with standards such as ISO 9001.
• Long-term evolutionary support and maintenance.
• Ability to work both on-premise and in the cloud.

We work with institutions of every size, from early-stage fintechs to established financial organizations, adapting the team and methodology to each context.

Related content

To go deeper into some of the topics on this page, we recommend reading How to Modernize a Legacy System Without Disrupting Business Operations, where we explain in detail the incremental modernization strategy we apply in banking projects.