This is Ucupaint, an addon to manage texture layers for Eevee and Cycles. I already worked on this for years, so it works for Blender 2.79 as well as the modern version of Blender.
You can visit the wiki to learn more about this addon, it’s not 100% complete but I hope it’s enough to get you started.
I know Blender will have similar native functionality like this addon in the near future, but nevertheless, I hope you can still have fun with this addon! 
Video Tutorials:
Many thanks, very useful!
Thank you!
Thanks all for all the comments. 
I just updated the first post to include an intro video tutorial.
After months of work, Ucupaint 1.1 is finally released! There are a lot of new features like UDIM support, bake other object channels, update notification, Blender 4.0 support, and tons of bugfixes!
I just added an option to use denoniser when baking AO to layer. It uses compositor to do the job. Here’s the comparison of the previous baked AO and the new baked AO with denoise on.
Since ucupaint 1.1 has branch selector, you can try the master branch directly from ucupaint UI here.
Now ucupaint can use image alpha as a mask. This is similar to the clipping mask in Photoshop. Please use the master branch if you want to test it.
Quick demo of painting anime eyes using ucupaint:
Quick demo of painting a torn cape using ucupaint
Now ucupaint can use backface as a mask. Be aware since the backfaces are sharing UV space with the front faces, you won’t be able to bake the channel into a single texture.
Edge detect is now available as a mask. You can use this to create some kind of procedural edge wear.
Ucupaint 1.2 is released! There are a lot of new features like baking denoiser, custom bake target for channel packing, realtime edge detect mask, Blender 4.1 support, performance tweaks, and more! https://github.com/ucupumar/ucupaint/releases/tag/1.2.0
I’m just going to feel and evaluate it for now, but it seems to me that this is a very worthwhile tool. This will help to realize the idea of “the whole pipeline without leaving blender” 
Thank you! Yeah, I like all my workflow to be inside blender. My goal is to make texture painting as easy as possible while still being flexible to any workflow. 
Anyway, Ucupaint 1.2.1 is just released. It’s a maintenance release with bugfixes and performance improvements. Ucupaint already has auto-updater, but if anyone still hasn’t installed it yet, here’s the link: https://github.com/ucupumar/ucupaint/releases/tag/1.2.1
EDIT: Ucupaint 1.2.2 is also just released since 1.2.1 has some problem with normal map https://github.com/ucupumar/ucupaint/releases/tag/1.2.2
Ucupaint 1.2.3 is just released! It fixes gamma color on layer preview mode and finally you can select any images outside of ucupaint node for texture painting. 
Here’s the link to download:
I’m finally back in the Blender sphere and I stumble in to find this - bravo, this is amazing utility for painting! I had no problems figuring out what to do to get started which is often the case with the painting addons that I’ve used before. Easily one of my favorite additions to my painting experience now, thank you so much!
