To make mods and game assets I use several applications. All of these are listed below.

Blender (free/donation) https://www.blender.org/	Typically used for creating and working with 3D meshes, materials and UV mapping, and exporting these as well.
Materialize (free) https://boundingboxsoftware.com/materialize/	A simple image-to-material tool for making new texture maps out of a diffuse map.
Topaz Gigapixel AI (paid/subscription) https://www.topazlabs.com/	This upscale tool can upscale any low-resolution image/texture to very high resolution without losing image quality.
GIANTS Editor (free) https://gdn.giants-software.com/	The primary tool for working inside GIANTS Engine for Farming Simulator modders.
GIANTS Texture Tool (free) https://gdn.giants-software.com/	A simple file-drop-to-convert tool to generate readable DDS files primarily for textures used in mods for GIANTS Engine/Farming Simulator.
Paint.NET (free/paid/donation) https://www.getpaint.net/	Another commonly used application for simple image editing, layer blending, adding various effects, and can also be used to make new textures from scratch.

Blender Add-Ons

For Blender, I use several add-ons that are available through Blender directly. From Blender Market, I use the following add-ons:

Quick Baker https://blendermarket.com/products/quick-baker	Quick Baker is an exceptional PBR texture-baking addon that brilliantly utilizes Blender’s native baking operator for baking PBR, Mesh, Principled BSDF, and Cycles maps.
Extreme PBR Nexus (2K version) https://blendermarket.com/products/extreme-pbr-addon-for-blender-279-2	This is a quick material tool. The user doesn’t need to use material nodes or shader nodes. It’s also suitable for playing with various materials, and this tool comes with 1800 different materials.
Smartify Nodes https://blendermarket.com/products/smartify-nodes	A tool for working with materials in Blender that has similar features to Extreme PBR, such as dragging and dropping preset materials onto meshes.
BagaPie Assets (full version) https://blendermarket.com/products/bagapie-assets	Natural and architectural assets for Blender can be dropped directly into the scene. These are mainly high-poly assets that also can be transformed into low-poly assets if needed.
Quick Landscape https://blendermarket.com/products/quick-landscape	This is somewhat of an old add-on that is useful for generating quick terrain landscapes in Blender from highly customisable presets.