Immersivity

Bits and Chisels - Turn Blocks Into Small Bits With Chisels; Build All The Things.
CIT Resewn - Re-implements MCPatcher's CIT (custom item textures from optifine resource packs).
Clean F3 - Removes useless information from the debug screen.
Cloth Config API - Configuration Library for Minecraft Mods.
Cubes Without Borders - A mod that allows you to play Minecraft in a borderless fullscreen window.
Cull Leaves - Adds culling to leaf blocks, providing a huge performance boost over vanilla.
DashLoader - Launch at the speed of light.
Dynamic FPS - Reduce resource usage while Minecraft is in the background or idle.
Essential - Boost your Minecraft. Play together without a server. Customize your character. And more.
Enhanced Block Entities - Reduce FPS lag with block entities, as well as customize them with resource packs.
Fabric API - Lightweight and modular API providing common hooks and intercompatibility measures utilized by mods using the Fabric toolchain.
FabricSkyboxes Interop - FabricSkyBoxes Interoperability for MCPatcher/OptiFine Skies.
FabricSkyboxes - Allows resource packs to define custom skyboxes.
FastAnim - Speeds up entity animation calculations.
FastQuit - Lets you return to the Title Screen early while your world is still saving in the background.
FerriteCore - Memory usage optimizations.
FeyTweaks - Mod for optimizing signs and beacons.
Geckolib - A 3D animation library for entities, blocks, items, armor, and more.
ImmediatelyFast - Speed up immediate mode rendering in Minecraft.
Immersive Portal Gun - Portal Gun with Immersive Portals.
Immersive Portals - See through portals and teleport seamlessly.
Ksyxis - Speed up the loading of your world.
Language Reload - Reduces load times and adds fallbacks for languages.
Lithium - No-compromises game logic/server optimization mod.
Memory Leak Fix - A mod that fixes random memory leaks for both the client and server.
Mod Loading Screen - An advanced loading screen with the loading progress of mods.
Mod Menu - Adds a mod menu to view the list of mods you have installed.
Model Gap Fix - Fixes gaps in Block Models and Item Models.
Noxesium - Improves client performance and play experience on large multiplayer servers.
Pehkui - Lets you change the size of most entities, shrinking them smaller or growing them larger.
ToolTipFix - Fixes Tooltips from runnning off the screen.
[EMF] Entity Model Features - EMF is an, OptiFine format, Custom Entity Model replacement mod available for Fabric and Forge.
[ETF] Entity Texture Features - Emissive, Random & Custom texture support for entities in resourcepacks just like Optifine but for Fabric.