The Overwatch Workshop, which allows players to create new modes with robust tools and rudimentary programming, has given rise to all sorts of unexpected oddities: a Smash Bros. clone, airplane races, portal guns, Mercy reinventions, and heaps more. The most popular mode of all, though? Uno. Yep, the card game.
Source: Kotaku – Overwatch Workshop’s Most Popular Mode Is The Card Game Uno