This small exe converts a RPG Maker XP autotile into an image which you can easily use to create your own autotiles in GMS2.
The tool is available as a .exe
Why focusing on RPG Maker XP autotiles? Autotiles from later RPG Makers are more condensed (contain less tiles) and, as a result, when you draw a map using them, they look "too square". I always thought RPG Maker XP autotiles helped create better looking maps. That is specially true when you use nature-related tilesets, like forests or sand.
I may update this to support autotiles from later RPG Maker versions.
WARNING! Each tile must be 32x32. So, the input image must be 96x128 pixels! Again, this only works with RPG Maker XP autotiles!