The List

OUTSIDE OF GAME (Not a plugin!)

-Blender
The very basic thing needed. It'll be needed for all sorts of modding things unless you have fancy paid tools to do it with instead. Highly recommend learning it all in blender!
Link: https://www.blender.org/download/

-Textools
A great method for modding and such. If you want to place animations into it you'll need to know the paths themselves. Just go to
Tools > File Operations > Import File
In order to import any pap you've made. It can also export the very same way and is a great way to extract paps even from mods if you import the mod first! Just do the same process as before with a small change
Tools > File operations > Export File!
Link: https://github.com/TexTools/FFXIV_TexTools_UI

-XAT
Very useful for checking animations outside of launching the game.
Also practically required to make animations using blender!
Link: https://github.com/Etheirys/XAT

-FFXIV Explorer
Extremely useful for finding different paths. The public official version is sadly missing a lot from its resource section. Namely after stormblood but you can find better filled out lists from other mod makers and even on different forks. Typically this is most useful for beginners and will end up rarely used by people who have done it for longer times but it remains useful throughout.
Fact its not a plugin is also quite the plus! Just remember to load file 040000!
Link: https://github.com/goaaats/ffxiv-explorer-fork

-(For 3ds Max) Multi Assist
While XAT supposedly works with HKX's as well. I've noticed it being a great deal more complicated to get working right. Multi-assist is fantastic at working with HKX's though doesn't have all the bells and whistles that XAT has. If you have any issues with animations not exporting quiiiite right from 3ds max. Use this!
Bonus fact. Using Multi Assist and XAT interchangably works as a wonderful global converter. Once an animation is a pap it can easily be extracted as either an HKX from Multiassist or an FBX from XAT for their respective best programs! Mulitassist=3ds | XAT=Blender
Link: https://github.com/ilmheg/MultiAssist

NOW FOR THE PLUGINS!

-Penumbra
A basic mod that lets you add and remove mods on the fly. I shouldn't need to say more on just how helpful this will be towards making animations!
Repo: