Are you tired of people sending you Farmville and Mafia Wars invitations on Facebook?  Or are you that friend that sends them to everyone?

One of these games, 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.

And with a whopping 400 million Facebook users to appeal to, the maker of these games is sure to be cashing in.  As a matter of fact, in all, more than 65 million people play Zynga games every day, according to media tracking company Developer Analytics.

But these aren’t your typical video games.  While most virtual entertainment attracts more of a male demographic, Zynga finds they typically have female users 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.

These games are also attractive because, as its creator designed, they are able to be played in tabs while you’re on a conference call, and then set aside; they don’t require constant engagement.

Some people aren’t fans of these games, however, and actually dedicate their statuses to dissing Mafia Wars, among others.

Whether you enjoy playing Farmville or not, one thing is for sure – as gaming expert Scott Steinberg put it, “We’re seeing, in many ways, a second renaissance for games”.