Most concurrent players on Steam for a videogame

As of 23 April 2019, the videogame with the most concurrent users on Steam was PlayerUnknown's Battlegrounds (PUBG). The game recorded an all-time peak of 3,257,248 players on 13 January 2018 and neither PUBG or any other game has managed to reach that level since - though it's worth noting that Epic's Fortnite (2017) is not available on Steam. The astonishing figure was reached during the height of PUBG's popularity and was confirmed by the Steam tracking site www.steamdb.info.