Freelance senior developer

~/stembera $ whoami

Stanley J. Stembera

Freelance Senior Full-Stack Developer helping teams stabilize, rethink, and evolve complex systems. Architecture, migrations, mentoring.

Trusted for the long haul: I’ve been working continuously with the European Space Agency (ESA) for over a decade on long-term systems where reliability, clarity, and consistency matter over time.
27+
years in software
10+
years with ESA
18
selected enterprise clients
4
languages spoken

About

I build and shape applications end-to-end — from user interfaces and interaction flows to backend services, data models, and overall system architecture.

A significant part of my work involves stepping into complex or legacy codebases and bringing them back under control — turning systems that have grown organically into ones that are understandable, maintainable, and reliable.

I’m typically brought in when a system needs to be rethought, stabilized, or gradually transformed — whether that means migrating legacy code, defining a clearer architecture, or helping teams find direction and confidence in their codebase.

I often work alongside developers as well, mentoring less experienced team members and helping raise the overall level of engineering within a project.


Focus

Architecture & direction

Defining clearer system boundaries, reducing accidental complexity, and helping projects move toward structures that make sense long term.

Legacy migrations

Gradual modernization of legacy applications without losing control of the system, the data, or the team around it.

Stabilization & cleanup

Taking systems that have grown messy over time and turning them into something more predictable, maintainable, and easier to reason about.

Mentoring

Supporting teams and junior developers through code reviews, technical guidance, and calm, practical engineering leadership.


Clients

Selected clients across aerospace, finance, telecom, manufacturing, retail, and software.

European Space Agency (ESA)Aerospace
AirbusAerospace
BMWAutomotive
Deutsche BankFinance
HSBCFinance
AllianzInsurance
AppleTechnology
MicrosoftSoftware
Nokia Siemens NetworksTelecom
Deutsche PostLogistics
OSRAMIndustry
FoxconnManufacturing
1&1 InternetInternet
Yettel BulgariaTelecom
Haufe-LexwareSoftware
DekaBankFinance
SinnerSchraderAgency
DouglasRetail
Aerospace Finance Telecom Automotive Manufacturing Retail Software

Contact

If you need help stabilizing a complex system, planning a migration, shaping a clearer architecture, or supporting a team through technical change, feel free to get in touch.

Karlstein am Main, Germany · Remote & on-site · DACH + CZ