High-performance computing (HPC) and cloud platforms provide complementary capabilities for scientific workflows, yet their integration remains challenging due to differences in resource management, data movement, security requirements, and hardware heterogeneity. These limitations hinder the realization of seamless hybrid computing within federated European environments. This paper introduces NOUS, a modular framework designed to enable HPC–cloud interoperability. The architecture is structured into four layers: user interfaces (e.g., Jupyter, Open OnDemand), workflow orchestration, resource management via the SLURM REST API, and container portability through Apptainer. The framework incorporates federated authentication, locality-aware data management, and standardized interfaces to support secure and compliant hybrid execution, including cloud bursting.