It's not quite popular to be honest :/

You had a few games or rock paper scissor but it never really made a hit. And there was a site or two of coin flip if I remember well.
But let's be clear: who here thinks coinflip is interesting or entertaining? --'

But there was also a game like agar.io! It's not exactly gambling but it's pretty funny!
The game wasn't bad and the idea was simple, it was an agar.io but instead of losing/winning points you were losing/wining satoshis ^^