Plugins and mods
Dalamud plugins add features to Final Fantasy XIV while it runs. You install them from the Plugin Installer, which the /xlplugins chat command opens once the game is started through XIVLauncher.
Each plugin is built for one Dalamud API level. When Dalamud moves to a new level, plugins built for the previous one show (outdated) in the installer and stay off until their authors update them.
Mods from Nexus Mods replace the game’s models, textures and sounds on your own client and are loaded with Penumbra or TexTools.
A collection of various game modifications
Electric Boogaloo - ♪ A whole new chat, a new fantastic chat window ♪
You do not talk about Fight Club, same for Submarines
Displays a list of valid gear pieces beside hints in the Fashion Report minigame.
A searchable mob database with spawn locations for Beastmaster, Blue Mage, or hunts
Automatically hides UI elements.
Take total control over your HUD.

SE friend list sucks.

Before StatusTimers, my buffs/debuffs were a mystery. Now, it's a well-organized history!
See every item you and your party pick up, as it drops.
Create custom map markers on the map/minimap! Like <flag> but permanent.
Lets you use the mouse wheel to switch tabs (like LB/RB on controllers do).

Yes. Still up. Press it.
Mouselook without holding right-click.
Control what's playing on your computer within XIV!

Hides every quest icon above NPC nameplates, sortable by type, with peek and toggle hotkeys.
Your loading screens, your way!

Customize quest objective text and popup layout.