Free, open-source participatory platforms like Decidim or Consul were designed by the 15M’ citizen activists in Spain. Initially implemented in Barcelona and Madrid, these platforms are spread in many countries. Castells has not examined the institutionalization of the 15M’s offspring, and thus we aim to contribute by studying the rollout of the Decidim platform in Catalan municipalities. We examine its disruptive potential along three democratic dimensions: transparency, participation and deliberation. Our study combines in-depth interviews and an online questionnaire administered to public officials in charge of the platform and analyses the levels of participation on the platform. The research shows elements of managerial continuity: the most valued goals are transparency, organisation of information and the collection of citizen proposals, rather than deliberation and transfer of sovereignty towards citizens. However, the platform forces administrations to consider individual citizens’ inputs, increases citizens’ proposals and initiatives, and brings in new participant publics. Furthermore, democratic innovation is being pushed ahead by a networkof activists and technological experts that continuously improve the platform and function as a counter-power (Castells, 2015, 2016).