  We propose a design for philanthropic or publicly-funded seeding to allow
(near) optimal provision of a decentralized, self-organizing ecosystem of
public goods. The concept extends ideas from Quadratic Voting to a funding
mechanism for endogenous community formation. Individuals make public goods
contributions to projects of value to them. The amount received by the project
is (proportional to) the square of the sum of the square roots of contributions
received. Under the "standard model" this yields first best public goods
provision. Variations can limit the cost, help protect against collusion and
aid coordination. We discuss applications to campaign finance, open source
software ecosystems, news media finance and urban public projects. More
broadly, we offer a resolution to the classic liberal-communitarian debate in
political philosophy by providing neutral and non-authoritarian rules that
nonetheless support collective organization.
