Longships is a Viking-themed plunder/trading game. Players start in the North Sea with an empty Longship each, surrounded by four countries: Denmark, Norway, Scotland and England. Players have to start with plundering at least one country each in order to get some initial resources to trade with. Trading is driven by differences in the countries' resources; each country produces 2 out of the 4 resources Cloth, Furs, Thralls and Mushrooms. Nearby countries differ on one resource only, while countries on opposite sides of the North Sea have a totally different set of resources. Long-distance trading is thus more profitable, but also more dangerous as changing weather conditions can make open sea-traveling fatal.
The countries themselves are weak in defense and easy to plunder. However, plundering a country weakens its trading potential, so that Vikings need to defend countries they build their trade on from Vikings plundering. Plundering a country also makes its population hostile to you, so that you can't build or repair Longships there, making you more vulnerable on expeditions to those countries. The key to success is thus to keep your hostilities at an optimal level.
Resources gained from trading or plundering can be sacrificed to the gods in order to gain additional actions. Sacrificing Thralls to Odin gets you new fresh men to throw into the fights, sacrificing to Thor lets you change the weather conditions, get yourself a beneficial trade wind or sink your foes with mighty storms. Mushrooms make you go berserk and fight and plunder more efficiently, while Freya helps cities grow and prosper and give more trading opportunities.
Resources can also be used to build new Longships, increasing the Viking's trading and military power. Just like in real life, the winner at the end of the game is the player with the most Longships.