Software Developer · PCB Designer · Founder
I build mobile apps, web platforms, and custom hardware from Berlin — and I ship all of it myself.
Abitur and the HPI Schülerkolleg both completed in 2026. Currently building cactusio full-time.
Six domains, one habit: shipping things that actually work.
Mobile
Flutter & Dart for production iOS and Android apps — built, deployed, and maintained end to end.
Web
Storefronts, dashboards, and custom backend systems — frontend to database.
Hardware
Custom boards for smart-home sensors and IoT devices, from schematic to prototype.
Security
DDoS protection, hardened auth, and responsible data handling in everything I ship.
Smart Home
Hardware and software that make spaces smarter, built from a genuine hobby.
Founder
cactusio and Hoppercraft — two companies founded during school.
Based in Mahlow, near Berlin — building cactusio full-time.
About
I'm Julius, 18, a software developer, PCB designer, and founder from Mahlow, near Berlin.
Education
Certificates and transcripts available on request.
Based in
Just outside Berlin. Founder, developer, and strength-training enthusiast.
The fitness app my two-person team has spent the last year building. Live on the App Store now.
Flagship app
Corely reads every set you log and projects it forward: strength forecasts, muscle balance, streaks, and gym leaderboards.
Progress & forecasts
Muscle balance
Set logging
Rest timer
Gym leaderboard
What else I've been building alongside Corely.
Web app used statewide to calculate 10th-grade final grades.
A universal air-quality sensor board, designed in KiCad.
The Schülerfirma I founded at Grace Hopper Gesamtschule.
Websites and full e-commerce systems for small businesses.
My own company — products for healthier living, built and shipped by me.
I'm not building cactusio to maximize profit. I'm building it so people are genuinely satisfied with what they use.
Where Corely and cactusio stand right now.
Launched and tested with real users.
Corely 26 is live on the App Store. Android is in open beta on the Play Store.
Use app revenue to obtain CE certification for PCB products like Juno 1.
Sell certified health and smart-home hardware under cactusio.
Running two companies as a student isn't free. Here's what I cover:
Covered by freelancing — building websites and shop systems for small businesses.
Open to freelance work, collaborations, or just a conversation about your next idea.