Automation and industrial mass production, particularly in sectors with low wages, have harmful consequences that contribute to widening wealth disparities, excessive pollution, and worsened working conditions. Coupled with a mass consumption society, there is a risk of detrimental social outcomes and threats to democracy, such as misinformation and political polarization. But AI, robotics and other emerging technologies could also provide a transition to community-based economies, in which more democratic, egalitarian, and sustainable value circulations can be established. Based on both a review of case studies, and our own experiments in Detroit, we derive three core principles for the use of computing in community-based economies. The prefigurative principle requires that the development process itself incorporates equity goals, rather than viewing equity as something to be achieved in the future. The generative principle requires the prevention of value extraction, and its replacement by circulations in which value is returned back to the aspects of labor, nature, and society by which it is generated. And third, the solidarity principle requires that deployments at all scales and across all domains support both individual freedoms and opportunities for mutual aid. Thus we propose the use of computational technologies to develop a specifically generative form of community-based economy: one that is egalitarian regarding race, class and gender; sustainable both environmentally and socially; and democratic in the deep sense of putting people in control of their own lives and livelihoods.