IN ST. LOUIS, in a poor black neighborhood of housing projects, brick rowhouses, and vacant lots north of downtown and aside the Mississippi, residents have access to a network of help that money can’t buy. Money, in fact, is not accepted. To obtain assistance—someone to fix a ear, watch a baby, move furniture, or stay with an infirm parent— residents must themselves contribute a service of their own to the “resource exchange.” Residents who aren’t well enough to make “deposits,” but who may well need to make withdrawals, can gain credits when volunteers from suburban churches and synagogues contribute labor in their name. It is a system that involves more than 4,000 people, 70 percent with annual incomes below $10,000. They keep track of their “balance” through a computer network with its own ATM-style cards, good at terminals at local stores, designed with the help of volunteer computer industry consultants.