Zynga Inc., a company that sells imaginary tractors and other make-believe goods in online games, plans to raise some very real money from public investors.
After weeks of speculation, the San Francisco start-up—maker of “FarmVille,” “CityVille” and other games played on Facebook’s website—on Friday filed for an initial public offering in a deal that could value it as high as $20 billion, said people familiar [...]




