Here you can find a list of Forge mods with links to their Fabric alternatives.

Major Mods Originally On Forge

The Aether (A Reimagining) (not complete)

Applied Energistics 2

Better Animals Plus

BetterNether

Bewitchment/Witchery

Botania

BuildCraft (in progress and not publicly available)

Charm

Chisel & Bits

ComputerCraft/CC: Tweaked

Create (in progress)

Deep Mob Learning

DimensionalDoors

The FTB Suite

FTB Chunks

FTB Quests

FTB Ranks

FTB Teams

FTB Ultimine

Galacticraft (in progress)

Hardcore Questing Mode

Just Enough Items/Not Enough Items

KubeJS

Morph

Mystical Agriculture (stuck in 1.16)

Oh The Biomes You'll Go

OpenCubicChunks (in progress)

Fabric versions are branches for versions 1.16 and above.

OptiFine

Pixelmon (in progress)

Refined Storage 2 (in progress)

Storage Drawers

Tech Reborn

The Twilight Forest (in progress)

WorldEdit

YUNG's Mods

YUNG's Better Caves (stuck in 1.16)

YUNG's Better Dungeons

YUNG's Better Mineshafts

YUNG's Better Strongholds

Minor Mods Originally On Forge

Antique Atlas

Artifacts

AtomicStryker's Infernal Mobs

Bedspreads

Cannibalism

Chipped

Comforts

Conjuring

Dank Storage

Environmental Creepers

Extra Alchemy

Outvoted

Goblin Traders

Prefab

RandomPatches (stuck in 1.16)

RSWires

Secret Rooms

Stoneholm

Storage Network

Soul Shards Respawn

Sound Physics

Tropicraft (stuck in 1.16)

VoxelMap

Waystones

Whisperwoods

Worse Barrels

Xaero's Minimap

Xaero's World Map

Originally Fabric

Some other high quality mods made originally for Fabric that you should definitely check out.

Adorn

BetterEnd

Blockus

Carpet And Its Addons

Carpet

Carpet Extra

Video explaining its features

Ecotones

Masa's Mods

Litematica

MiniHUD

Tweakeroo

Modern Industrialization

Mo' Structures

Origins

Rat's Mischief

What About Everything Else?

Architectury is a project which abstracts calls to the Forge and Fabric API allowing mod creators to write a single piece of code for both mod loaders, reducing the amount of code duplicated to support Forge and Fabric.

Patchwork is a project aiming to re-implement the entire Forge API into Fabric, so that any Forge mod jar can simply be patched, and then run as if it were a Fabric mod. Its development is currently on hold.