Painting in real-time on 3D models is a lot of fun to do, it is a nice reward once you have finished all the other things you have to do in the creation of a 3D model.
The first software I used whilst learning how to UV map and texture 3D models was Blender 2.79. I’ve been using 3D Coat to do my 3D texturing more recently because I find it intuitive to use and the UV mapping and baking features are easy to use as well. The interface for painting is similar to most digital painting programs I’ve used which decreased the learning curve for me a little.
I found Blender a little harder to use for painting, but I have heard that future versions will be improving the 3D painting features and there are add ons to make painting easier in Blender as well. I might give it another go. I am considering trying out Mixer at some point as well because it looks like a nice program on par with Substance Painter and it is free so why not?
There are other options out there, including some interesting add ons for Blender. I will link to them here for your own perusal.
Free all in one texturing tool from Quixel. You can use models from the Megascans library or load your own objects. Unreal users can use all the objects in the Megascans library.
A multi purpose texturing tool. Substance products were acquired by Adobe a few years ago. You can still get a perpetual version on Steam though.
ArmorPaint is a stand-alone software designed for physically-based texture painting
Agama Materials is a free procedural material and 3D painting software.
3D Coat is a digital sculpting and 3D painting application.
3D sculpting and painting tool. Freeware and professional version available. Still in development stage so it may be buggy, but the developer is working on improving the software. Perhaps one to watch for future.
Open source 3D creation. Blender is the free and open source 3D creation suite. It supports the entirety of the 3D pipeline — modeling, rigging, animation, simulation, rendering, compositing and motion tracking, video editing and 2D animation pipeline.
There are some commercial painting add ons for making painting in Blender more intuitive by adding layer support and other features.
Primarily a digital sculpting application with 3D vertex painting (PolyPaint) features and UV map creation as well.
3D digital painting and sculpting software
High-resolution digital 3D painting and texturing.
Modo is an all in one 3D modelling, texturing and rendering software.
The new version of Toolbag released in 2020 now has texturing ability.
Developments in new software
A non-destructive painting mode is being implemented into a future version of the free and Open Source Dust 3D.
Affinity Photo is working on 3D texturing features for a future version.
Thanks for reading!