Velocity

Rendering and Graphics

Sodium: A complete replacement for the Minecraft renderer that significantly increases frame rates and reduces micro-stuttering.
Sodium Extra: Adds extra features to the Sodium settings menu, such as animations and particle toggles.
Sodium Iris: The bridge that allows you to run shaders while using Sodium's performance engine.
Reese's Sodium Options: Reorganizes the Sodium settings menu into a cleaner, more navigable layout with tabs.
Sodium Shadowy Path Blocks: Reintroduces vanilla-like smooth lighting to non-full blocks (e.g. dirt paths and how they have dark shading when directly next to a full block) when using Sodium.
ImmediatelyFast: Optimizes the rendering of immediate mode graphics, which primarily improves performance when viewing the UI, containers, and entity text.
Entity Culling & More Culling: Prevents the game from rendering objects and entities that are hidden behind walls or outside your field of vision, saving system resources.
LambDynamicLights: Adds dynamic lighting to the game, allowing held items like torches to illuminate the environment without requiring a shader pack.
Continuity: Enables support for connected textures via built in texture packs, allowing blocks like glass and sandstone to blend together seamlessly for a cleaner look.

Lithium: A general-purpose optimization mod for the game's internal systems, improving physics, AI, and block ticking without changing vanilla behavior.
FerriteCore: Specifically designed to reduce memory (RAM) usage by optimizing how the game stores block states and models.
ModernFix: A comprehensive suite of bug fixes and performance improvements that targets long loading times and high memory consumption.
BadOptimizations: Despite the name, this mod improves performance by removing or streamlining redundant rendering calls in the game's code.
Better Block Entities: Changes the way chests, signs, and other block entities are rendered to make them less taxing on the GPU.

Concurrent Chunk Management Engine (CME): Enhances the game's ability to process world data on multiple processor cores, leading to faster world loading and smoother exploration.
Very Many Players (VMP): Optimizes the way the game handles networking and player data, which is essential for maintaining performance on servers with high player counts.
Scalable Lux: A complete rewrite of the Minecraft lighting engine. It speeds up the calculation of lighting data, which reduces lag during world generation and helps prevent "lighting updates" from causing frame drops while you are moving through the world.

Essential Mod: Adds social features including a friend list, world hosting for easy multiplayer without a server, and an in-game cosmetics system.
Simple Voice Chat: Provides a high-quality proximity voice chat system for multiplayer environments.
3D Skin Layers: Replaces flat 2D skin overlays with 3D versions, giving player skins more depth and detail.
Wavey Capes & Capes: Adds physics to capes so they flow naturally with movement rather than remaining stiff.
Chat Animations (Smooth Chat): Makes the chat box feel more modern by adding smooth sliding animations to incoming messages.
Chat Heads: Displays the face of the player next to their message in the chat window.

Debugify: A massive collection of fixes for hundreds of small bugs and performance "papercuts" present in the base game.
Language Reload: Allows you to change languages instantly without the game freezing or reloading all assets, and adds a search bar to the language menu.
XP Clumps: Groups experience orbs together into a single entity to prevent lag when large amounts of XP are dropped at once.
Mod Menu: Adds a screen to view and configure all installed mods from the main menu.
Required APIs: Background libraries that allow all the above mods to communicate with the Fabric loader and each other.

note: not all features are supported in every version of Minecraft and are going to change over time.