The advent of COVID-19, with its stay-at-home orders keeping workers from eating out and its social distancing recommendations making them leery of running to the grocery store, is jump-starting the online grocery shopping business. Some retailers are struggling to adjust to the sea change, with Amazon.com (NASDAQ: AMZN) apparently overwhelmed by the sudden popularity of its Amazon Fresh and Whole Foods online ordering services, and unable to keep up with demand. Still, analysts forecast that as much as $20 billion in online grocery business could be up for grabs for the companies that manage to figure this out. Image source: Getty Images. Walmart (NYSE: WMT) could be the biggest beneficiary. According to a report just out from App Annie, the self-described "leading global provider of mobile market data," the Walmart Grocery app is now the No. 1 most downloaded app for ordering groceries online. From March 29 to April 4, 2020, reports the analyst, consumers downloaded 106 million shopping apps, up 15% from the equivalent period in January 2020, before the coronavirus appeared on the scene. Of those downloads, 14.4 million happened in the U.S. (up 20% from January), and Walmart Grocery downloads in particular shot up 460%. Downloads of the Me@Walmart app, used by in-store workers, were also up significantly -- 220%. In contrast, Amazon's shopping app, the second most downloaded shopping app which began the period with "an incredibly high existing install base," lagged Walmart's pace of downloads by 20 percentage points. 10 stocks we like better than Walmart Inc.When 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 Walmart Inc. 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 March 18, 2020 John Mackey, CEO of Whole Foods Market, an Amazon subsidiary, is a member of The Motley Fool's board of directors. Rich Smith has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Amazon and recommends the following options: short January 2022 $1940 calls on Amazon and long January 2022 $1920 calls on Amazon. The Motley Fool has a disclosure policy.Source