The Workshop is available now on the PTR.

Create games in ways previously unimaginable with the Workshop! The Workshop is a simplified game scripting system that expands the customization features available in the Game Browser. Within the Workshop, you’ll create a Script to add Rules and unique play Conditions on top of the established Overwatch game modes you already know and love. Rules can do many things, like change how a hero’s movement and abilities work, modify how players are damaged or healed, or even display text under certain circumstances.

One hot game mode you can create is Molten Floor, where your hero will catch on fire if they’re on the ground:

Check out the dev update for more details:

https://news.blizzard.com/en-us/overwatch/22938941/introducing-the-overwatch-workshop

Source: Blizzard