Blizzard has been saying for years that they would like to introduce a map maker into Overwatch, or at the very least something to help players create their very own content. The first phase of this project arrived alongside the custom game system quite a while ago, and even though the whole thing was incredibly basic, it showed that there is a great deal of interest in modding Overwatch.
While the map maker is still nowhere to be seen, I am very happy to announce that Blizzard has now released a fairly comprehensive scripting tool in order to give players a chance to create their very own game modes and events, as well as play the ones created by the community at large. The Workshop system is currently being tested on the PTR, so if you would like to see it for yourself, simply change your region to "PTR" on the PC version and you'll be able to create your very own game modes in no time.
Before you do so, allow me to share with you the recently posted developer update discussing the Workshop. It should give you a pretty good idea of what you're getting yourself into and what exactly the Workshop is capable of. Have a gander:
Even though the Workshop is a bit limited in terms of what you can do, it's without a doubt an amazing addition, and one that will only get better once the community gets more comfortable using it. After all, it's not every day you get to see someone try and recreate Katamari Damacy by combining Wrecking Ball with a slowly expanding Graviton Surge!
So if you have a bit of free time, I'd heartily recommend going to the PTR and seeing what the community has created. It's mostly still unpolished, but as you'll see for yourself, there is already a bunch of great modes out there, especially if you're looking to train your aim or movement.
Have fun!