In addition to the base game, The Sims 3 features 11 optional expansion packs and nine stuff packs. As of 2015, it has sold over 7 million copies, making it one of the best-selling PC games of all time.

The Sims 3 was released for Windows PCs and Mac OS on June 2, 2009. Moodlets can be triggered by specific events, proximity to certain areas or objects, or by very low or very high motives. Moodlets can have a positive, negative, or neutral affect on a Sim's mood. Sim needs are also updated, with much of the functionality of these needs replaced or augmented by moodlets. These traits influence a Sim's behavior and wishes, including their lifetime wish. The Sims 3 replaces the points-based personality system of The Sims and The Sims 2 with a system based on unique traits. The Sims 3 also introduces the Create a Style tool to the series, which allows players to change the patterns and colors of objects and clothing, and copy styles between different objects. The Sims 3 features robust customization options through an expanded build mode and Create a Sim. The Sims 3 is the first game to feature an open-world concept: players are no longer limited to having a single lot loaded at a time, and Sims are able to move about and explore an entire town without triggering a loading screen.

The Sims 3 keeps many of the innovations introduced by its predecessor, but adds several new features. Like other The Sims games, The Sims 3 focuses on creating and controlling virtual worlds filled with simulated people called ' Sims.' The Sims 3 is the third main title in The Sims series of video games.

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