Valve's Steam platform has broken it's own record of 18.5 million concurrent gamers online yesterday, with a whopping 18.8 million gamers all playing online simultaneously. 

It's around 300k more than the previous record, which was set 2 years ago, according to SteamDB. The reason behind this though seems unclear, there wasn't any particular game launch or other event happening at the time.

.@Steam has broken its record for most concurrently online users that was held for two years. Previous record was 18,537,490 users. It's still increasing!

But there's about 1 million less players actually in-game (≈5.8mil vs ≈7mil two years ago).https://t.co/D6WDHbz0B4

— Steam Database (@SteamDB) February 2, 2020

The previous record occurred when Playerunknown's Battlegrounds was at the height of it's popularity, so yesterday's figures are a mystery. It seems folks just really wanted to play games yesterday.