Under the joint bid, Urban Muse would allow New Yorkers to invest up to $1 million in the retail component. “Retail is such an amenity, I wanted it to be woven into the community,” said Mr. Lolli-Ghetti, although he worries that city officials handling the request for proposals may consider public participation “a gimmick.”

He’s not sure crowdfunding is suited to large, complex projects. “In real estate, $10 million to $20 million projects are easy. But if you need $500,000 to buy a (small) property and put a local tenant on the street floor, you can’t do it. It’s too small for private equity.”

Mr. Goodman of Third Ward, the co-working and educational space in Bushwick, is a long-term leaseholder who said owning the building through usual lending would require putting 50 percent down in cash — or $7.5 million, an amount out of reach for now.

Buying it with the help of small investors is “something we’ve started to explore again,” he said. (Its Crown Heights commercial kitchen project opening next year is largely financed by Goldman Sachs.)

The Third Ward mailing list of 80,000 people, 3,000 members, 15 investors and thousands of students who have taken classes there over the last six years could be a ready investor base.

“Many of them would be very interested in different ways of participating,” Mr. Goodman said. “This is game-changing for small businesses like ours but also for the neighborhood. It’s bottom-up development instead of top-down, and that is totally unique. Nobody understands a neighborhood better than the people who live there or are stakeholders.

“To me, it’s like, why hasn’t this already happened?”