This post will serve as a portal for accessing all the tools I regularly utilize with concerns to Minecraft Data Pack and Resource content creation. This post may be updated.

Obligatory for Newbies: Data Packs for Dummies tutorial by Bertiecrafter

Side note: All of the downloadable software on this list is free and open source, with a large development community and userbase to ensure future updates and continuity. 7-Zip and GIMP are what I consider essential software due to their innumerable uses, and VS Code is my go-to for anything programming related that doesn't require a compiler.

Data pack software:

7-Zip	Free and Open Source file archiving program for creating .zip and .mcpack files. Also useful for exploring other filetypes (like native Minecraft .jars in your %appdata% directory)
Visual Studio Code	Free and Open Source integrated development environment (IDE) useful for a variety of programming-related tasks
language-mcfunction	An extension for VS Code that highlights text to be more comparable to Minecraft's command syntax colors
Data-pack Helper Plus	An extension for VS Code that adds a variety of useful shortcuts and auto-completions for data pack files

Data pack webware:

misode's datapack generators	Useful web tools for generating structured JSON files for data pack projects
mcstacker nbt generators	Useful web tools for generating commands with complex NBT data
Minecraft Tools generators	Useful web tools for things that require visual feedback that the previous generators don't offer. While some tools on this site are made redundant by the above-listed sites, I find the text generators to be especially useful for preview purposes.
Minecraft Wiki	Useful for referencing various game mechanics and behaviors

Resource pack software:

GIMP	Free and Open Source image editing software, useful for literally everything (like making thumbnails/cover art), but also great for modifying textures
Blockbench	Free and Open Source low-poly modeling software, useful for creating custom models and posing

Resource pack webware:

rtm516's texture pack converter

Note: Before converting textures drop the pack version in pack.mcmeta to 5 (or 6 if using the 'Experimental conversion' feature) Useful web tool to convert Minecraft Java texture packs to Minecraft Bedrock version. Does not always work with all textures, you may need to use an archive explorer (like 7-Zip) to extract the generated .mcpack file and make specific alterations to files by referencing the current official Mojang Bedrock Texture releases.

PMCSkin3D

PMC's web tool for easily editing entity textures in a 3D environment