High-end IT services
Stefan Köllner — over 30 years of software engineering. Web, backend, mobile, custom domain software, Linux operations, AI-assisted tooling — built and shipped from Hamburg, Germany for mid-sized companies, agencies and specialised industries across Europe.
About
stuf.rocks is the service brand of ndtss/Stefan Köllner — based in Hamburg, with over 30 years of software engineering across web, desktop applications, embedded data acquisition, mobile app development, Linux server operations and AI-assisted tooling. The shop offers concrete, scope-bound engagements; larger custom work runs via direct coordination.
What's delivered here is not generic agency output — it's code from a specialist who chooses the stack, writes the code, operates the servers, and answers the emails. Architecture principles (loose coupling, testability, extensibility) are non-negotiable: the result is software you can still change two years from now.
Also behind ndtss — NDT Software Solutions, with products in use across Europe and the GCC. Over a decade of hands-on Linux server operations rounds out the toolbox.
Expertise
Fast, accessible, server-rendered websites and web apps. Static-first where it fits, dynamic where it has to. SEO and i18n built in.
Backend services from a single Flask script to a multi-tenant API. Built for explainable performance, clean migrations and operability — no surprise scaling cliffs.
Bespoke applications where off-the-shelf software doesn't fit: data acquisition, reporting, databases, data migration, device integration, signal processing, industry-specific tooling. Delphi (Master Developer certified), Python, .NET on request.
Production Linux clusters — web, mail, monitoring, backup. A proven master/slave HA architecture, available for your stack.
Custom Model Context Protocol (MCP) servers and AI-augmented developer workflows. Not chatbots — real tooling that connects an LLM to your repos, data and operations.
Server hardening, code audits, dependency review, restore-tested backups. Small enough to ship in days, serious enough for production.
Industries
Mid-sized companies that have outgrown their hosting provider, agencies that need an engineer instead of a freelancer, start-ups that need their first production stack done right, specialised industries (NDT, instrumentation, niche manufacturing) that need software built around their domain.
In-house web, backend, server consolidation, AI-assisted internal tools.
Engineering capacity for complex projects: Astro, custom backend, infrastructure.
First production stack done right — architecture that survives the first hire.
NDT, instrumentation, lab automation, niche manufacturing — domain-native software.
Practical websites and tooling without the agency overhead.
Continuity of engineering style across products and services.
Services
Each service has a fixed scope and a fixed price. Larger engagements are composed of multiple packages. To book, open the packages page or write to hello@stuf.rocks.
Custom software engineering across the full stack — backends, domain-specific applications, device integration and embedded data acquisition. Architecture-first, written to remain maintainable in year three.
For non-destructive testing software in production: ndtss.de — products in use across Europe and the GCC (eddy current acquisition, signal processing, reporting). Project references on request.
Production Linux operations for your stack. From a single VPS to a multi-host master/slave HA cluster — built and run with the same care as a production environment.
Modern, lightweight web sites — static-first with Astro 6 + Tailwind 4 (or Next.js where it fits). Built for speed, accessibility and SEO from day one. All-inclusive packages bundle hosting, mail, cloud and ongoing care.
Endpoint and server monitoring with managed RMM. Patch management, remote support, helpdesk ticketing — everything needed to keep a fleet of devices and servers running predictably.
Architecture reviews, stack decisions and technology audits — done by someone who has shipped production systems, not someone selling slides. Decision-grade output you can act on.
Stack
Next step
Tell me the task in two paragraphs. If a package fits, link it. Reply usually within 1–2 working days.