The COLLECTiEF project will enhance, implement, test and evaluate an interoperable and scaleable energy management system based on Collective Intelligence (CI) that allows easy and seamless integration of legacy equipment into a collaborative network within and between existing buildings and urban energy systems with reduced installation cost, data transfer and computational power while increasing data security, energy flexibility and climate resilience. This is done through developing software and hardware packages to install and smart up buildings and their legacy equipment on large scale, meanwhile, to maintain simple and robust communication with the energy grid. The provided scalable solutions will integrate seamlessly with existing legacy equipment and will facilitate demand-side management of multiple buildings, enhancing energy flexibility and resilience in urban areas.