August was a huge month for game sales in the United States. Software spending was up 16 percent year-over-year to $285 million, according to industry-tracking firm The NPD Group. Tom Clancy’s Rainbow Six: Siege was one of the games driving that growth. It finished the month as the No. 3 best-seller behind Madden NFL 19 and Monster Hunter: World.

Rainbow Six: Siege debuted December 2015. But age is nothing but a number when it comes to games-as-a-service. If you need evidence of that, just ask 60-month-old Grand Theft Auto V, whose Grand Theft Auto online continues to push sales. What really matters to gamers these days is that a game seems like it is active and interesting. In August, publisher Ubisoft was able to prove just that about Siege.

“Tom Clancy’s Rainbow Six: Siege climbed the chart from the ninth-ranked position in July to become the third best-selling game of August,” NPD analyst Mat Piscatella said. “Performance was driven by the free-play period that ran August 16-to-20 in conjunction with the Six Major Paris 2018 Esports tournament and associated retail and digital promotion.”

The first one is free

Publishers and developers are turning to free play weekends more often. These events enable anyone to download a game and enjoy all of its features for an entire weekend without having to pay any upfront price. Once the weekend is over, you lose access. Or, you can pay and keep all of your progress so far.

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These promotions seem like a nice treat for people who want to try a game, but the strategy is making money.

One of the reasons this model works is because it enables people to get online and play with their friends who may already own and love the game. That’s especially important for Siege, which has 35 million players. Siege’s fans love it, and that is infectious. It’s so powerful that if someone gets a taste of it with their friends on a long session on Saturday night, they may end up spending the money to keep playing when the week begins.

Ubisoft, Electronic Arts, and Activision Blizzard are reluctant to make their games free-to-play. But they are experimenting with different business models outside of the $60 release and the $100 Deluxe version. Rainbow Six: Siege starts at $15 for a basic version of the game — that makes it easier for people to convert on those free weekends. I would expect to see a lot of these same strategies for a game like Battlefield V not long after it launches.