A lucrative business or product. Primarily heard in UK, Australia. That mobile dating app has proved to be a real money-spinner for the developer—it's making them more money than anything else they've launched before.
a money-spinner
(British & Australian)
a business or product that makes a lot of money for someone Cookery books are becoming a real money-spinner for the publishing industry.
spinner
n. a bullet. Harry the Horse’s shot sent a spinner into Lefty’s gut.