At this point, no matter what country you're in, you're probably trying to find things to do while staying inside. It's undoubtedly this that has led to the incredibly impressive figure of 20 million people using Steam at once. The figure comes via Steam Database and a tweet they put out on the matter. They also tagged the tweet with #coronavirus, because it's pretty obvious why everyone is playing games at the moment.
The moment came at 14:30 GMT on Sunday, March 15th, when the 20,313,451 people were all online at once. That's just on Steam itself though, of those, 6,384,829 people were playing games at the time. Most of these players where on Counter-Strike: Global Offensive, which has seen a resurgence in recent weeks. Of course, this doesn't include the gaming platforms on PC other than Steam, so you can assume that between the Epic Store, Uplay, GOG, and all of the other launchers around, that the numbers were actually higher than this still.
The Epic Store would be a particularly interesting number what with many schools closing down or parents simply keeping their kids home. You have to assume that Fortnite is seeing a huge boon to its player base at the moment, especially given the fact that the game is free. It might even be a good time to learn some of the Fortnite dances as a way of keeping fit while staying indoors. We've no idea how many calories Flossing for an hour would burn, but it's better than nothing.
On the subject of free games, Call of Duty: Warzone has already seen a rather astonishing 15 million people visit its gassy shores, so you can expect that to remain popular as well. Whether or not there'll be a diversification of the kinds of games played would be interesting, maybe not to you, but the stats in these times are fascinating for a great many people. The other games in the Most Played category on Steam include other shooters like Destiny 2, PUBG, and Rainbow Six Siege.
Of course, DOTA 2 is currently riding very high as well, with around half a million people playing at the time of writing this piece. There are also smaller games like Terraria, RimWorld, and even Garry's Mod doing rather well at the moment. It's highly likely that more people will be playing as the coronavirus has more and more people staying indoors over the coming months, so at least we can keep ourselves entertained by breaking records on Steam users.