SkyBlock was a popular Minecraft map created in 2011. You spawn on a floating island and survive until you inevitably get bored and quit. You start off with a tree and a chest containing a block of ice and a bucket of lava. You needed to make a
cobblestone generator, expand your island, and do whatever the hell you wanted. In July of 2019, PewDiePie and
CinnamonToastKen used their big brains to make a cobblestone generator in their SkyBlock series.
In June of 2019, a prototype game called 'Hypixel SkyBlock' was released on the
Hypixel server and it gained immense popularity. The game is a new take on the original SkyBlock, but it requires a lot more grinding and has a dedicated gambling feature. Did I mention it'll waste hours of your life? The game was released during Minecraft's resurgence, so that helped with it's popularity and vice versa.