Why: Companies are building ­businesses inside platforms like Facebook.

Key innovation: Its social games offer people a new way to interact online.

Technology:

The company designs casual games that can be played in brief spurts over a long period of time. Its games include a social element, giving users a new way to interact with friends online. It has become well known for titles such as Farmville, Mafia Wars, and the recently launched CityVille.

Market:

Zynga's games are aimed squarely at users of social-networking sites such as Facebook, but last year the company began developing versions of its games to be played on mobile devices like the iPhone. The company now claims to have over 200 million monthly active users across all games.

Strategy:

The company makes money by charging users for virtual goods, such as virtual tractors that make it easier to till the land in Farmville. Though it makes some of its money from advertising, it says that 90 percent of its revenue comes from the virtual goods, which are reportedly purchased by a million users each month. Analysts estimate that the company earned half a billion dollars in revenues last year.

Challenges and Next Steps:

Zynga is still heavily dependent on Facebook and its users, but it has been branching out to other platforms. In June, the company’s games made their first appearance on Apple’s App Store and can now be played on the iPod Touch, the iPhone, and the iPad. Given Google’s reported $150 million investment into Zynga, the company's games should soon appear in Google’s Android marketplace. Whatever the platform, Zynga will have to continue to find effective ways to promote its products, and to keep users engaged despite a flood of similar offerings.