The Richest Gaming Start-Ups You've Never Heard

Screengrab via ModernWar
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GREE

Estimated daily revenue from Modern War: $361,789

With over 10 million users, Modern War's fans could make up a small country. Of course, that's part of the game's appeal: players team up for missions in which they compete to take over the world.

Japanese developer GREE has produced other combat games such as Knights & Dragons and Crime City and it's one of Japan's largest social networking services.

Analysts attribute the company's success to its track record of investing in developers.