Research from SuperData estimates that the average millennial spends $112 per month on gaming content. The levels of engagement and monetization for video games trounce nearly every other entertainment medium under the sun. Even more enticing, the industry is poised for long-term growth as more people take up gaming as a hobby and monetization avenues including advertising and in-app purchases continue to gain ground. For investors looking to stake a position in the growth of interactive entertainment, Zynga (NASDAQ: ZNGA), Glu Mobile (NASDAQ: GLUU), and Ubisoft Entertainment (OTC: UBSF.Y) stand out as the industry's best stocks to buy in September. Let's take a closer look at these three companies. Image source: Getty Images. 1. Zynga Zynga has orchestrated a comeback over the last five years by completing successful acquisitions and focusing on getting more revenue out of its core franchises. The company surpassed Activision Blizzard's King Digital division to become the biggest mobile games publisher in the U.S. by revenue in July, and it still has plenty of room for growth over the long term. When Zynga announced it was purchasing Turkish developer Peak Games at the beginning of June, the company said it expected the integration to boost its daily active users on mobile platforms by more than 60%. The $1.8 billion half-cash, half-stock deal closed early in July and quickly helped make Zynga the top U.S.-based mobile publisher. Adding to the significance of that distinction, video games have seen elevated engagement amid conditions created by the coronavirus. The market has never been bigger. Maintaining engagement and boosting profitability for core franchises has helped the company increase sales and profitability in recent years, and Zynga will have the opportunity to apply its life-cycle and monetization magic to Peak's popular titles. There's also a good chance that Zynga will make additional acquisitions with this same strategy in mind. Even after completing its purchase of Peak Games, Zynga has a net cash position of roughly $500 million. Combined with the fact that the company is seeing substantial growth for operating cash flow and has the option to use stock as a component in future deals, the strong balance sheet means there's room to approach further acquisitions that can accelerate sales growth. Zynga has a promising collection of video game franchises and development studios capable of creating hit new content, and the company is in a good position to benefit from long-term growth of the video game industry. 2. Glu Mobile Glu Mobile is a video game publisher that makes casual-focus games for smartphones and tablets, and its shares look particularly enticing after a spat of recent sell-offs. While the S&P 500 has rallied over the last three months, Glu Mobile stock is down double digits across the stretch. GLUU data by YCharts Glu stock took a significant hit early in August after the company published second-quarter results that arrived with an unexpected loss, news of setbacks for one of the company's in-development projects, and a delay for another title. In addition to lagging the broader market, Glu is the only major Western video game publisher to see its stock decline over the last several months. The company's outlook is much better than that performance might imply. The earnings miss largely stemmed from elevated player acquisition spending and the company recording more business as bookings than sales than the market had anticipated. While revenue rose roughly 40% year over year in Q2 to reach $133.3 million, bookings soared 79% and reached $182 million. The extra bookings should show up as sales in the months to come. News of weak user feedback for an early test version of a story-based game platform the company has been working on may have ultimately soured the market on what was a pretty good quarter in many respects. However, long-term investors shouldn't get too hung up on this setback. Glu is looking attractively valued trading at roughly 22 times this year's expected earnings and sporting a market cap of $1.3 billion. Glu has a stable of dependable franchises including Covet Fashion, Design Home, MLB Tap Sports Baseball, and Kim Kardashian: Hollywood that should help shore up near-term performance. It also has a collection of studios working on supplemental content and new franchises and a strong balance sheet opening the door to acquisitions. Glu's path to success looks a lot like what Zynga has accomplished over the last five years. With the stock looking cheaply valued in the context of its growth potential, Glu is a hot buy this September. 3. Ubisoft France-based video game publisher Ubisoft has seen its stock performance lag far behind that of rivals including Activision Blizzard, Take-Two Interactive, and Electronic Arts over the last year. It's not hard to see why. On the other hand, Ubisoft looks cheaply valued compared to many of its competitors, and the market is underestimating the company at present. Ubisoft owns franchises including Assassin's Creed, Rainbow Six, and Far Cry. While it doesn't currently have a property that can match the popularity of Take-Two's Grand Theft Auto or Activision Blizzard's Call of Duty, the company has a solid collection of bankable franchises and development studios capable of churning out hits. Underperformance for some key titles and substantial release delays have put a damper on sales and earnings, and this weakness has naturally translated to the company's stock performance. But there's a good chance Ubisoft will turn it around. Sony and Microsoft are set to launch new video game consoles later this year, and Ubisoft should benefit from the chance to introduce new properties and reinvigorate existing ones thanks to the hardware upgrade cycle. The publisher also has plenty of opportunities to benefit from the long-term growth of mobile, streaming-based gaming, and esports. Ubisoft has a market cap of roughly $10 billion and trades at about 3.5 times this year's expected sales and 17.5 times expected operating income. It's fair to say that the publisher has looked a lot weaker than Activision Blizzard and Take-Two over the last year, but Ubisoft is cheaply valued at present -- and investors looking to ride gaming industry momentum should consider adding the stock. 10 stocks we like better than Glu MobileWhen investing geniuses David and Tom Gardner have a stock tip, it can pay to listen. After all, the newsletter they have run for over a decade, Motley Fool Stock Advisor, has tripled the market.* David and Tom just revealed what they believe are the ten best stocks for investors to buy right now... and Glu Mobile wasn't one of them! That's right -- they think these 10 stocks are even better buys. See the 10 stocks *Stock Advisor returns as of August 1, 2020 Teresa Kersten, an employee of LinkedIn, a Microsoft subsidiary, is a member of The Motley Fool’s board of directors. Keith Noonan owns shares of Activision Blizzard, Glu Mobile, Take-Two Interactive, and Zynga. The Motley Fool owns shares of and recommends Activision Blizzard, Microsoft, Take-Two Interactive, and Zynga. The Motley Fool recommends Electronic Arts and Ubisoft Entertainment and recommends the following options: long January 2021 $85 calls on Microsoft, short January 2021 $115 calls on Microsoft, long January 2022 $75 calls on Activision Blizzard, and short January 2022 $75 puts on Activision Blizzard. The Motley Fool has a disclosure policy.Source