Custom software
with AI built in,
not bolted on.
AI-powered web and mobile apps, ERP and CRM systems where AI drafts the follow-ups, reads the documents and handles the paperwork, and your team approves the result. 14+ years of senior .NET engineering for clients across Europe and the US.
public class Solution {
async Task<Result> BuildAsync() {
var stack = new Stack(
backend: "C# .NET 10",
frontend: "Blazor",
mobile: "MAUI Hybrid",
cloud: "Azure",
ai: "Azure OpenAI + Gemini"
);
return await stack
.WithAI(humanApproval: true)
.DeployAsync();
}
}
What we build
From a single AI feature to a complete platform: we design, build, launch and maintain software for companies in Croatia and abroad.
AI built into your workflow
AI that drafts emails, classifies documents, turns plain-language input into data and summarises reports, with a person approving every result. Running in production in our own products.
AI-poweredWeb applications
Business web apps and portals in Blazor and .NET: dashboards, self-service portals, booking and workflow tools.
WebMobile apps
Android and iOS apps with .NET MAUI, published on Google Play and the App Store, with push notifications and offline use.
MobileWeb shops
Online stores with card payments, subscriptions, invoicing and stock, connected to your accounting and delivery services.
E-commerceIntegrations
Connecting the systems you already use: REST and SOAP APIs, webhooks, payments, e-signatures, email and data sync.
APIsERP systems
Custom ERP modules for orders, inventory, work hours, scheduling and reporting, built around how your company actually works, with AI entry from plain language.
OperationsCRM systems
Sales pipelines, contact management and AI-drafted follow-ups, or integration with Salesforce, HubSpot and Pipedrive.
SalesComplex systems
Multi-tenant platforms, real-time systems and high-volume data processing with a clean, maintainable architecture.
ArchitectureCloud and maintenance
Migration to Azure, CI/CD pipelines, monitoring and ongoing support after launch.
AzureProducts and projects
in production
Our own products and solutions we've built for clients in IoT, legal tech, workforce management, enterprise support and more — across Croatia, the Netherlands, the UK and the US.
Followloop — Email CRM with AI follow-ups
A CRM that fills itself from your sales email: it matches replies to leads, tracks stages and next steps, and AI drafts follow-ups the user approves. Works with Microsoft 365, Gmail and IMAP, with Stripe billing and HubSpot, Pipedrive and Zapier integrations.
getfollowloop.comZvrk — AI platform for kindergartens
Web and mobile platform connecting kindergarten staff, management and parents: communication, attendance, reports and menus, with AI helping teachers with daily paperwork.
zvrk.hrŠihterica — Time tracking with AI
Work-hours tracking compliant with Croatian labour law: web management and a mobile app, leave requests, project hours and reports, and AI entry from plain language ("worked from 8 to 4").
sihterica.com.hrEpTeam — Workforce Management Platform
Staffing and workforce management platform with a web app, a cross-platform mobile app and real-time updates, built on a shared Blazor component library.
IoT Device Management Platform — 10,000+ Devices
Scalable web application for real-time monitoring and management of thousands of IoT devices, with automated CI/CD deployment pipelines.
High-Performance Support Ticketing System
Upgrade and optimization of a real-time ticketing system with SignalR for live updates, dramatically reducing resolution times.
Critical Data Synchronization Optimization
Custom T-SQL algorithm for a mission-critical sync process, drastically improving data availability across the organization.
Estate Planning — Legal Counsel Application
Integration of Stripe payments, Calendly-like scheduling, and calendar systems into a legal counsel platform for estate planning.
SAP Data Extraction Tool
Purpose-built tool for efficient retrieval and analysis of business data from SAP databases, enabling faster reporting and insights.
Real-Time Scoring for Street Race Competitions
Live scoring system with real-time result updates for race competitions, improving scoring accuracy and audience engagement.
We also connect your
systems with the best
Beyond custom development, we integrate your systems with leading platforms — from AI and payments to document management, CRM and communication tools.
Azure AI Services
Azure OpenAI, Cognitive Services, Computer Vision, Language Understanding, Speech
AI / MLGoogle AI / Gemini
Vertex AI, Gemini API, Natural Language, Vision, custom models
AI / MLDocuSign
E-signatures, workflow automation, envelope API, templates
DocumentsOmnidocs
Document management, workflow, digital archive, compliance
DocumentsStripe
Online payments, subscriptions, invoicing, Connect — production-proven
PaymentsTwilio
SMS, voice, WhatsApp, video — programmable communication APIs
CommunicationSendGrid / Mailchimp
Transactional email, marketing campaigns, audience segmentation, analytics
EmailSalesforce
CRM integration, lead management, custom objects, Apex triggers, reporting
CRMCustom Integrations
Don't see what you need? We build custom REST/SOAP APIs, webhooks, middleware, SAP, ERP/CRM connectors — any system, any protocol.
Anything you needA proven stack,
with AI on top
From C# backends to Blazor frontends, from Azure cloud to AI services — battle-tested, modern technologies for robust solutions.
Azure OpenAI
GPT models, drafting, summaries, structured output
Google Gemini
Natural-language input, extraction, classification
Human-in-the-loop AI
AI suggests, people approve — safe automation
C# / .NET 8+
High-performance backend, REST & GraphQL APIs
Entity Framework
EF Core, Dapper, migrations, data access layer
SignalR
Real-time communication, WebSockets, live dashboards
OAuth / Identity
JWT, RBAC, IdentityServer, authentication
Blazor
Server & WebAssembly, C# in the browser, SPA
.NET MAUI Hybrid
Cross-platform mobile & desktop applications
JavaScript / Vue
TypeScript, Vue.js, Lit, jQuery — reactive UIs
Responsive UI
Mobile-first design, component-based, Pinia/Vuex
SQL Databases
Oracle, MS SQL, PostgreSQL, MySQL — tuning & security
PL/SQL
Stored procedures, triggers, advanced Oracle querying
Redis
Caching, session management, pub/sub messaging
Elasticsearch
Full-text search, logging, analytics
Azure Cloud
App Services, Functions, Service Bus, Queue, Storage
DevOps / CI-CD
Azure DevOps, GitHub Actions, Jenkins pipelines
Docker / K8s
Containerization, orchestration, scaling
Terraform / IaC
Infrastructure as Code, ARM templates
Git
GitFlow, code reviews, GitHub, GitLab, Azure Repos
Monitoring
Application Insights, Grafana, Log Analytics
Software Architecture
DDD, Clean Architecture, CQRS, enterprise patterns
Microservices
Loosely coupled, independently deployable services
Event-Driven
RabbitMQ, Azure Service Bus, message queues
Serverless
Azure Functions, event triggers, pay-per-use
Agile / Scrum
TDD, Kanban, SOLID, JIRA, code quality
Vedran Jandrasincec —
14+ years of engineering
The founder and lead engineer behind 4J Solutions brings a proven track record across banking, consulting and enterprise IT — working with industry leaders across Europe.
- Developed various business applications using PHP & MySQL
- Built solutions tailored to specific business needs and workflows
- First professional role — foundation in full-stack web development
- Developed 50+ new features for the bank's intranet using Oracle SQL and C# .NET
- Enhanced loan application systems using PL/SQL, streamlining the process for users and staff
- Created 100+ dynamic document generation tools, automating creation and reducing manual errors
- Resolved 1,000+ production tickets annually, significantly improving system stability
- Optimized sprint planning processes, boosting team efficiency by 31%
- Built and maintained 10+ web applications using C# .NET, Vue.js, and Azure
- Improved system reliability and speed by 20% through code and infrastructure optimization
- Reduced development time by 50% by introducing modern frameworks and practices across teams
- Mentored junior developers, improving team skills and knowledge transfer
- Architected and delivered a full-featured webshop platform — end-to-end e-commerce solution
- Built a building & property management system for real estate operations and tenant management
- Developed an ERP system for the construction industry, streamlining project and resource management
- Led code reviews and optimization efforts, increasing system performance by 20%
- Mentored junior developers, fostering knowledge-sharing and technical growth
Experience across key industries
You work directly with
the engineer who builds it
4J Solutions is a specialized software engineering company with 14+ years of experience designing, building and optimizing complex systems. No account managers and no hand-offs: the person you talk to is the one who designs the architecture, writes the code and keeps it running. We cover the full lifecycle, from architecture and AI features to deployment and ongoing support, for clients in Croatia, the Netherlands, the UK and the US.
Frequently asked questions
How much does custom software cost?
It depends on what we're building, so there is no fixed price list. We usually price by project or scope rather than by the hour: with AI in our workflow, hours say little about the value you get. Hourly arrangements are possible by agreement. Tell us what you need and you'll get a concrete quote.
How long does it take to build an application?
Smaller projects take 2–4 weeks with AI in our workflow. Larger systems depend on complexity and are delivered in phases, so you see working software from the first weeks.
Can you add AI to our existing system?
Yes. We connect your current system to Azure OpenAI or Google Gemini through an API, without rewriting it. AI drafts, classifies or summarises, and your team approves the result.
Is our data safe when using AI?
Yes. We use Azure OpenAI in an EU region, your data is not used to train AI models, and everything is processed in line with GDPR.
Who owns the source code?
That is agreed in the contract. You can own the full source code, or we can license the software to you, depending on the project and budget.
Do you offer maintenance after launch?
Yes. Monitoring, updates, bug fixes and new features after launch, on terms we agree together.
Do you work with clients outside Croatia?
Of course. We work remotely with clients across Europe and the US, in English and Croatian.
What does the process look like?
An intro call, then a specification and estimate, then development in short iterations with a demo after each one so you can steer the result, followed by launch and ongoing support.
Is the first consultation free?
Yes. The first call is free and with no obligation: tell us what slows your team down and we'll tell you how software and AI can help.
Do you sign an NDA?
Of course. We sign an NDA whenever needed, before you share any details about your project.
Can you take over or modernise an existing application?
Yes. We take over existing systems, upgrade older .NET applications to modern .NET, migrate them to Azure and add AI features along the way.
Let's discuss
your project
Get in touch
Have a project in mind? Feel free to reach out — we respond within 24 hours.