Sure, none of it's real. But the overwhelming popularity of so-called social gaming -- simple games that let people play with their friends on networking sites such as Facebook -- is changing the face of video games, experts say.

And as the maker of popular titles like FarmVille and Mafia Wars, San Francisco, California-based Zynga has ridden the games' skyrocketing popularity to the top of that emerging market.

For Zynga founder Mark Pincus, the formula for gaming success on Facebook, MySpace and other sites was as simple as it might seem counterintuitive: create simple games that people like but can easily set aside.

"We built the games so they could be played in a tab on your browser while you're on a conference call," said Pincus, a veteran Web entrepreneur who created Zynga in 2007.

Of course, they've been helped by the massive growth of Facebook, where the games are so popular they've spawned "fan" pages devoted to complaining about having to watch friends play them.

Facebook, with its 400 million users, is where the vast majority of people play FarmVille and Mafia Wars along with other Zynga titles like FishVille, Vampires, Café World, YoVille and Zynga Poker.

In all, more than 65 million people play Zynga games every day, according to media tracking company Developer Analytics.

Zynga's top title, FarmVille, is played by an estimated 75 million people each month -- roughly equal to the number who have played the classic arcade and desktop game Tetris during its entire existence.

The massive growth was satisfying but not altogether surprising to Pincus, whose previous startups had included Freeloader, a Web-based information-gathering service; tech-support company SupportSoft; and Tribe.net, an early social networking site from 2003.

He said that starting the game company, which he named after his late English bulldog, was an effort to fill what he considered a surprising void in most people's daily Internet use.

"I thought in 2007 that something had gone oddly wrong with the whole Internet experience," Pincus said. "I would have thought games would have been one of the top two or three experiences people had on the Internet."

What Pincus got right, according to gaming expert Scott Steinberg, was a sort of return to the "golden era" of games like Pac-man and Super Mario Bros.

"Video games actually appealed to a huge cross-section. They appealed to everybody," said Steinberg, publisher of DigitalTrends.com. "What happened is, as we went through the mid-'80s to the mid-2000s, you started to see gaming become more incestuous in terms of 18- to 34-year-old males making games for people just like them."

By contrast, three of Zynga's top five games -- FarmVille, Café World and FishVille -- have mostly female players, with many players outside the traditional 18- to 34-year-old range.

Those games all operate on the same basic premise. Starting with a simple farm, fish tank or restaurant, the player works to make it bigger and fancier, sharing items with friends and helping each other along the way.

Some of Zynga's early titles simply mirrored existing board and card games. It was Mafia Wars -- in which players team up to whack other gangs -- that first exhibited what would become the hallmarks of social gaming: simple, single-player action that's enhanced by teamwork.

With FarmVille, that formula would become complete.

Players plant virtual crops that can be harvested hours, or days, later. Along the way, they invite online friends to become their neighbors and help each other by sending gifts or helping with the farming. There's no way to "win," but players take satisfaction in building big, fancy farms that they can showcase to their friends.

"A farm is something that is internationally understood and known. It's cross-cultural, cross-gender, cross-age," Pincus said. "A great social game should be like a great cocktail party. If you want it to appeal to absolutely everyone you invite, it has to be broad in its content so that everyone gets it."

Not that Zynga's success has come without criticism.

With hundreds of smaller companies vying for a piece of the social gaming market, some rivals have accused Zynga of using its hefty venture capital to crowd out less-financed competitors.

Many of its most popular games, including FarmVille, are similar to pre-existing games from smaller companies, a fact Pincus dismisses by noting that video games have always fallen into genres with similar titles from competing companies.

Psycho Monkey LLC, the makers of Mob Wars, filed a lawsuit claiming that Mafia Wars ripped them off. Zynga settled that case in August, said a spokeswoman for the company.

Zynga also was hit with complaints and lawsuits over its original business model, which let players earn in-game rewards for things like signing up for a credit card or video-rental membership.

Critics said some of the offers amounted to scams, leading players to download unwanted software or unwittingly sign up for memberships that appeared stealthily on their phone bills.