SAVERS DO NOT get much in the way of interest from their banks these days. But a different logic seems to apply to borrowers, who still often pay double-digit rates for credit—if they can get it at all. That has attracted a number of outfits offering to connect those who need cash with those who have a surplus of it. The rapid growth of such “peer-to-peer” lenders has been one of fintech’s most visible successes. The biggest such firm, Lending Club, based in San Francisco, listed its shares in December to a clamour reminiscent of the 1999 tech boom.