What’s the most popular video game these days? If you think it’s Halo: ODST, Batman: Arkham Asylum or Wii Fit, think again. While high profile console games are hogging the consumer spotlight, Zynga’s FarmVille – a free-to-play Facebook game about tilling soil and tending crops in a virtual farm – has quietly amassed more than 58 million active players.

For anyone counting, that number easily surpasses the sales figures of the best-selling console video game of all time: Nintendo Wii juggernaut Wii Sports, which has only sold about 45.7 million copies to date.

The number of people who play FarmVille is still growing. Let’s put it this way: More people play FarmVille than watch Oprah. Players have generated more than 40 million farms (20 times more than the actual number of farms in the United States), own more than 500,000 tractors, and conduct more than 80 million harvests each day. So far, $321,000 in real cash has been raised for charity through the selling of an exclusive kind of sweet potato in the game. FarmVille supplements its free-to-play model by letting players purchase special items in exchange for real-world currency.

So why do so many people enjoy doing virtual chores in their spare time? Mark Skaggs, VP and GM of Social RTS Studio at Zynga – FarmVille‘s San Francisco-based creator – says the farm theme is actually one of the game’s biggest advantages.

“Everyone knows what farming is. They ‘get’ farming, whether it’s because they read about farming at school or have actually lived on a farm,” Skaggs explains. And in FarmVille, where crops ripen just a few hours after they’re planted, the process feels more like entertainment than work. “People like the zen-like feeling of clicking on their plots to do plowing, leaving for a while, and coming back later to see that their parsley has grown.”

Crops that aren’t tended regularly will wither and go brown, which gives players a strong incentive to come back and check in on their farm regularly.

Zynga understands the extremely powerful potential of social networks like Facebook to provide cheap, compelling entertainment in tough economic times. As soon as one friend starts playing FarmVille on Facebook, they recommend the game to other friends in their network, and news about their progress in the game appears in their news feed. Trying the game is literally a click away. It’s the best kind of free advertising.

It also makes the console business model look as outdated as records and CDs as compared to MP3s. “Games like FarmVille are very easy to get into,” Skaggs explains. “It’s totally different than having to go down to Best Buy, find the console game you’re looking for, spend 50 bucks, bring it home, and hope you like it. FarmVille is free to try, and free to keep playing if you like it.”

Before there were computer games, Skaggs argues, gaming was an inherently social pastime, whether it was playing sports outside or board games on a Sunday afternoon. Skaggs is convinced that FarmVille and social games like it will bring things full circle, by connecting people around the world and bring back “the experience of playing Monopoly around the dinner table.”