Here's an oddball that I'd never even heard of until recently; during the Russo-Japanese War of 1904-5, the Russians had no machine guns, but faced the Japanese who did. During the Siege of Port Arthur (in modern-day China, near the border with North Korea), a Captain Shemetillo came up with this weird thing, necessity being the mother of invention. A system of rods lets the bolts of all 5 rifles (Mosin-Nagants) be operated and fired simultaneously, while the "gunner" aims using the sights on the middle rifle. It's amazing what sort of work circumstances can produce