Two years ago, Scott Doyon saw the chance to organize a kind of concert that was unheard of in the Atlanta metro area. It was a remarkably homey concert for a city, defined primarily by its venue: front porches.

Doyon, a spiky-haired former musician, thought maybe 25 bands would sign up. He got 130. Spectators hopped the train to Decatur, a streetcar suburb of Atlanta, by the thousands. More than 100 porches throughout Decatur’s historic Oakhurst neighborhood hosted bands. “Where we ended up, bot…