Available for new opportunities
Mikael Marceniuk
Fullstack Developer
Building high-impact web, mobile, and backend systems at scale.
From billions of records to real-time failover, engineered to perform.
About me
Engineering systems that scale and deliver real impact.
I'm a fullstack developer with 6+ years of experience building web, mobile, and backend systems across betting, enterprise automation, and logistics.
I've worked on systems handling billions of records, built real-time failover infrastructure across microservices, and delivered features that drove measurable revenue growth.
I'm comfortable owning full delivery cycles, from architecture decisions to production, working independently or embedded in cross-functional teams.
Independent Projects
Featured Work
NexusCRM
Fullstack CRM built for businesses that rely on WhatsApp, Instagram and Facebook as their primary communication channel. Features real-time messaging, contact and pipeline management, and automated workflows.
Speaker Trainer for Business
AI-powered web app for deliberate speaking practice under professional pressure. Users record responses to high-stakes scenarios, receive automated feedback across 5 criteria, re-record, and see improvement between attempts.
Higher Up Business English
Landing page for the only company in Brazil with BELF methodology (Business English as a Lingua Franca). Built with Next.js and analytics and SEO.
Professional Timeline
Professional Experience
February/2025 — May/2026
Fullstack Developer
Upbet
- Delivered high-impact features for a regulated betting platform serving the Brazilian market, working across microservices, real-time systems, and fullstack development.
- Built an automated failover system across microservices on AWS that detects provider outages and switches in real time, ensuring continuous platform availability.
- Participated in a cross-continental migration of billions of records from EU to Brazil using AWS and Python, ensuring zero data loss.
- Developed a fullstack referral system in a 2-person team that drove approximately 10% revenue growth.
July/2022 — February/2025
Fullstack Developer
FaliFe Technology and Innovation
- Built and maintained mission-critical automation pipelines and internal systems for enterprise clients, eliminating manual workflows and improving operational visibility.
- Designed an automation pipeline integrating 3 databases with Lecom, DocuSign, and Feedz via REST APIs, reducing a 4-day process to 2 hours.
- Built a fullstack asset management system with NestJS and Next.js from scratch to replace Excel-based tracking, delivering instant reporting.
Capabilities
Technical Skills
Frontend
- React / Next.js
- TypeScript
- Tailwind CSS
- Framer Motion
- GraphQL Client
Backend
- Node.js / Bun
- Elysia / Hono
- Go
- REST / GraphQL
- WebSockets
Database
- PostgreSQL
- Redis
- MongoDB
- Drizzle / Prisma
- Supabase
Cloud & Infra
- AWS (EC2, S3, RDS)
- Vercel
- VPS / Caddy
- Nginx
DevOps & CI/CD
- Docker
- GitHub Actions
- Turborepo
- Terraform
- K8s
Contact
Let's work together
Open to freelance projects and full-time opportunities, local or international. I respond within 24 hours.