Collective self-consumption and waste energy recovery are appealing opportunities to tackle climate change, albeit complex to implement. Multiple stakeholders and objectives are involved; investment is needed in intermediate units whose ownership may be unclear and the space for feasible solutions – let alone that for optimal solutions – may be small, among other considerations. This chapter proposes a methodology to facilitate the technical design of energy community projects involving multiple stakeholders, typically producers and consumers in proximity to each other, and potentially connected by intermediate aggregators. The first and main innovation is OMEGAlpes, an open-source tool facilitating the use of mixed-integer linear programming for energy systems design. By means of anticipatory simulation, this tool optimizes the use of equipment throughout a project’s lifespan. The second innovation combines OMEGAlpes with multi-criteria analysis, putting forward a locally optimal design per stakeholder and criterion. Such assessment may include many quantitative criteria: energy, economy, exergy and environment, among others. The third and last innovation consists of a cross-analysis matrix and a multi-criteria radar, which represent overall performance and stakeholder convenience for each locally-optimal design. The three innovations are combined in an iterative procedure that determines the space of suitable solutions depending on stakeholders’ priorities, thus facilitating subsequent negotiations.