I build software that solves problems.
Hi, I'm Oskar — a freelance fullstack developer with 5+ years of experience. I build websites, mobile apps, backend systems, and APIs for clients who need reliable, well-crafted software. Whether you're a startup needing an MVP or a business looking for a custom web application, I can help.
What I Can Build For You
From simple landing pages to full-stack applications — here's how I can help bring your ideas to life. Every project is built with clean code, modern tools, and attention to detail.
Websites & Landing Pages
Fast, responsive websites for your business, portfolio, or project — built with modern frameworks for speed, SEO, and a great user experience.
Mobile Applications
Native Android apps with modern Material Design, or cross-platform with Flutter and React Native. From concept to Play Store deployment.
Web Applications
Full-stack web apps with authentication, data management, admin panels, and real-time features. Built with React, Next.js, or Astro.
Backend Systems & APIs
Scalable REST APIs, GraphQL endpoints, microservices, and database architecture using Spring Boot, Ktor, Go, and .NET.
DevOps & Infrastructure
Docker containerization, CI/CD pipelines, Linux server setup, and deployment automation to keep your applications running smoothly.
Custom Development
Need something specific? I'll work with you to understand your requirements and build exactly what you need — no project is too small.
Technical Expertise
Core technologies I use to develop production-grade software — from backend APIs and mobile clients to websites and infrastructure.
Explore full skillsetBackend & API
Designing and building production-grade server-side systems with modern frameworks, robust APIs, and clean architecture.
- Spring Boot
- Spring Data JPA
- Ktor
- ASP.NET
- Gin/Fiber
- Microservices
- REST API
- GraphQL
- gRPC
- SQL
Mobile Development
Crafting native and cross-platform mobile applications with modern frameworks and best practices.
- Jetpack Compose
- Material 3
- View Models
- Navigation
- Dagger/Koin
- Kotlin Flow
- Flutter
- Dart
- React Native
Web Development
Crafting responsive, cross-platform web applications with modern frameworks and best practices.
- React
- Next.js
- Gatsby
- Svelte
- Astro
- Tailwind CSS
- PostCSS
- SSR
- SSG
Infrastructure & DevOps
Managing containerized deployments, CI/CD pipelines, and Linux environments to ensure reliability and performance.
- Docker
- Linux
- GitHub Actions
- GitLab CI
- SQL
- ORM
Selected Work
Projects that showcase my skills — from open-source tools to client-ready applications.
LibrePass
A full-stack, open-source password manager with end-to-end encryption, zero-knowledge architecture, and a Kotlin/Spring Boot backend for multi-device synchronization.
- Kotlin
- Spring Boot
- Jetpack Compose
- Docker
- Integration Testing
Oskar Karpiński
This portfolio website — built with Astro 6, Tailwind CSS v4, and Material 3 design. Fully responsive, supports dark mode, and optimized for performance.
- Astro
- Tailwind CSS
- TypeScript
- Material 3
- SSG
Let's build something together
I'm available for freelance projects — from small websites to full-stack applications. Have a project in mind or just want to discuss an idea? Let's talk and see how I can help.