Decidim is a digital platform for citizen participation
It’s a free/libre and open-source web-based software, maintained by an extense and active community. It can be used in a public or private organisation, with hundreds or thousands of potential participants, such as a city council, an association, a university, an NGO, a trade union, a neighbourhood association or a cooperative.
Currently it's being used by the city of Barcelona, NYC, European Commission, Helsinki, the French Congress and Senate, and the Brazilian federal government among others.