Shweta Kohli has always paid her own way. Her straight-A average won her a full scholarship to San Francisco State University at the same time she worked a 40-hour week as a waitress at a cafe. But when she applied for a credit card after graduation, she was turned down because she had no credit history.

So three years ago, Ms. Kohli, now 34, joined a lending circle — a small group of people who chip in every month to lend money to one another at no interest. Managed by the Mission Asset Fund, a nonprofit group in San Francisco that works with credit-rating agencies, the circle offered Ms. Kohli something no bank would: a chunk of cash and a chance to build a credit score.

After faithfully making payments — and socking away enough to buy a 1997 Ford Mustang — she raised her credit score from zero to 789 in 26 months. Ms. Kohli, ever the striver, said: “My goal is to keep it at 850, the highest.”

While informal lending circles among families, acquaintances, co-workers and neighbors are familiar to hundreds of millions of people all over the globe, they are rarely recognized by mainstream financial institutions.