REEFLEX aims to generate niches of opportunities for new cross-sector energy services provided by SMEs and start-ups in demand side flexibility markets and to increase participation of energy consumers in demand side flexibility markets. The project develops a central interoperability platform and a catalogue of services with the capability of maximising distributed energy resources' flexibility while respecting the different end user profiles and needs along with the physical limitations of existing infrastructures. Additionally, the generation of a common operation market model together with AI-driven intelligence services and automation systems, enabled through the utilization of distributed ledger technologies for enhancing transparency and trust, will reduce market entry barriers and costs and achieve a higher participation from energy consumers. They will benefit from new revenues obtained through data and flexibility transactions, while enjoying innovative, personalized, data (intelligence)-driven services for smart, human-centric control of their assets in the frame of demand response or self-consumption. REEFLEX solutions, they will be demonstrated and cross-tested in 4 main demonstrators (Spain, Greece, Switzerland, Bulgaria) with different characteristics, allowing evaluation of their impact under alternative scenarios and integrating a variety of sectors, such as residential buildings, mobility, commercial establishments, industrial sites or data centres, among others. In addition, the services catalogue will be further replicated in three additional replicators across Europe to achieve wider coverage (Turkey, Portugal, Denmark) and adaptation, ending-up in a total of 7 countries for the whole project execution. These cross-tested demonstrators and additional replication campaigns are structured around 8 different use cases that cover a comprehensive set of consumer groups to participate in up to 12 demand side flexibility services.