Senior Application Developer (Freelance) – Legacy Systems

About the role

We are looking for a Senior Application Developer on a freelance basis to support the stability, security, and evolution of mission‑critical legacy applications for a client in Brussels. The role focuses on maintaining and modernising systems built with PowerBuilder, ASP.NET and SQL.

Key responsibilities

• Lead corrective and evolutionary maintenance of legacy applications.
• Drive continuous improvement initiatives for stability, security and sustainability.
• Own production activities, incident remediation and small‑scale developments.
• Collaborate with functional analysts to align technical solutions with business needs.
• Conduct technical analysis, identify risks and optimise performance.
• Support the progressive modernisation of legacy systems while adhering to established methodologies.

Required profile

• Proven senior‑level experience in application development and maintenance.
• Strong analytical mindset with proactive problem‑solving.
• Ability to work in a hybrid environment (minimum two days onsite).
• Professional proficiency in English; French or Dutch is a strong advantage.
• Familiarity with Agile methodologies is preferred.

Required skills

• .NET (expert level)
• PowerBuilder (expert level)
• PL/SQL (expert level)
• SAP SQLCA (expert level)
• Windows Services (expert level)
• Architecture Distribution Service (expert level)