I’ve gotten pretty far using FOSS tools when it comes to making games, but I would like something like Substance Painter so I can fully dabble into 3D.
Nothing AAA quality or very professional, I just want something that works good enough for my indie games lol.
- Blender for the texture painting - Material Maker for turning those textures into game engine ready materials. It’s also capable generating textures using noise and other patterns. Examples - Common Blender W 
 
- Armorpaint might be what you are looking for. Blender texture painting is nice, but Armorpaint is much closer to the substance painter experience. - Edit: For example, with Blender texture painting, unless you’re familiar with nodes, you would usually only set up one texture at a time. - Armorpaint also uses nodes, but it also uses a layer system just like substance painter. You can then modify the texture using nodes if you want to. 
- Never tried these but: https://armorpaint.org/ // https://github.com/armory3d/armortools - edit: Seems like Blender is capable of this too: https://www.youtube.com/watch?v=AnRQhH3fEDY 



