Essential Client but with way more quality of life features
These include:
Customizable Player Models
Ability to play with friends (if you have any lol) without server
Essential Mod cosmetics (alot of people use essential so they can see it)
Inventory Essentials (inventory managment tweeks)
Better recipe books (useful for potions)
Carpet mod (more creative commands)
Freecam (you can disable if it is against a servers rules)
Gamma Utils (configable fullbright)
JEI (better recipe book but always and mod compatable)
Litematica (schematic mod)
Lithium and Sodium (performence)
Ability to have custom capes
Replay mod (recording thingy)
Voice chat (self expanitory)
Tweekaroo (TWEEKS!)
Worldedit (edit the world...)