If another "swapper" finds the food appealing, they can simply claim it through the app and pick it up.
Mr Newman, a 25-year-old freelance financial writer in Seattle, said the idea for LeftoverSwap arose after a night of gorging on pizza.
He and co-founder Bryan Summersett bought too much pizza from their favourite Seattle pizzeria.
"In our quest to sample as many of the pizza toppings ... we overestimated our appetites," said Mr Newman.
The binge left them with a fridge full of leftovers and no place to store the excess.
"This got us thinking," he said. "If only there was a way to broadcast to our immediate area that there was perfectly good-to-eat pizza available."
Mr Newman said for as many people who hate the idea, there are those who love it.
"The first thing people think of when they hear the word 'leftovers' is some old soggy sandwich."
"[But] it can be used for all sorts of food: extra tomatoes from a garden, canned or boxed food and extra groceries," said Mr Newman.
Despite the app's novelty factor, Mr Newman said it aimed to address the serious issue of food wastage.
The London Institute of Mechanical Engineers, in its 2013 report Global Food; Waste Not, Want Not, found as much as 2 billion tonnes of all food produced globally, or about 50 per cent, ended up as waste.
Mr Newman said current food systems were inefficient.
"Because we waste so much, it's easy for small increases in efficiency to have a large effect.
"As the global population increases, it just makes sense to better match the supply and demand of food," said Mr Newman.
LeftoverSwap will be available in the English-language Apple iTunes app store, which includes New Zealand, from tomorrow.
Android and web-based versions are to come.
It isn't the first web-based food-sharing portal to be offered in New Zealand. Earlier this year ITM Fishing Show host Matt Watson launched freefishheads.co.nz to encourage fishers to give away unwanted fish heads instead of throwing them away.
