A MegaCollection Kits

★ marks things I personally have played and recommend. Please let me know of anything else I could add in the comments at the bottom.

One of the greatest Sonic fangames of all time, built on Doom Legacy

Main Website Forums Server Browser

It is recommended that you create an account on the forum before you download anything in order to follow the mods for updates.

Utilities

LauncherBlast2 reBoot for easier mod-loading. srb2dl is a command-line download manager. srb2srv is a CLI server browser. srb2bld can help compile alternate builds of the games (as shown below).

Alternate builds

SRB2 Uncapped PLUS adds Discord Rich Precense. SRB2NetPlus removes control lag when playing online. rphys overhauls the physics engine and gives the base characters new moves. SRB2 VR Mod adds what it says.

Other Websites

Wiki

Mods

Too many to reasonably count.

Maps

All Official Level Design Collabs ★ (formerly Contests). Also see the Unofficial Level Design Collabs (Link to forum member that hosts them) ★.

The Mystic Realm (Old Site) ArchPack The X-PACK Sol Sestancia Sol Sestancia 2 SSNIsland Chaos Domain SUGOI (Shut Up and Get On It) Logarithmic Train Zone Nu Angel Island Zone - Act 1 Angel Island Tour ★ Island Tour Dimension Glaber New Horizon Neo Palmtree Zone Equinox Sonic 2006 Emerald Coast Speed Highway SRB Dream Emulator Sweet Bro and Hella Jeff - the moive

Gameplay

The True Arena Snolf Super Run SRB2Randomizer Chaotic Edition VS. Metal Mode Paintbrush Sonic Paint Blast 3D foxBot Day/Night Cycle (Works with Werehog below)

Cosmetic

Jeck Jims' 3D Models Mega Paint Drive H-SRB2

Characters

Tweaks to Vanilla Roster

CrossMomentum Sonic Advance 2: Boostmentum MetAlt V. Maximum Overdrive

Alternate Versions of the Base Roster

Xtreme Junio Sonic S3 Sonic Adventure Sonic Modern Neo X Sonic Greeneyes Sonic New Bandages (Sonic Boom) Earless (SRB1 Sonic) Super Sonic Crystal Sonic Super Mystic Sonic HMS123311 Alt SSN Sonic Hard Sonic TA Tails (Tails Adventure) OVA Knuckles Chaos Knuckles Ugly Knuckles Plug-Hand Knuckles Amy Rose Pack Rose Gold Amy Magic Metal Sonic ChrispyChars (Pointy Sonic, Fluffy Tails) Max Control Pack Overhauled Legacy Trio (Hand Drawn, Less Unique, Chrispy Marriage)

Other Sonic Characters

Eggman (Eggpack) Egg Robo Mecha Sonic Sonic R Characters (Metal Knuckles, Tails Doll) Bean Honey Trip Shadow Silver Blaze RushChars (Blaze, Marine) Espio The Chaotix (Vector, Charmy,Espio, Mighty, Heavy, Bomb) Ray E-102 Gamma Werehog Advance Cream Tangle Whisper Surge

Crossover

Kirby Meta Knight Elfilin Super Mario Bros. (Mario & Luigi) Bowser Yoshi Kamek Vivian Pac-Man Crash Bandicoot Spyro Kiryu Kazuma Cacodemon DoomGuy Duke Nukem DeltaChars (Kris, Susie, Ralsei) Bubsy the Bobcat Meat Boy Sash Lilac Plague Knight Windows The Kid Among Us Impostor Henry Stickmin Pig from Angry Birds Taz the Tasmanian Devil FL Studio Chan

OCs

Sonic.EXE Eggette "Omelette" Robotnik Maimy Team Kinetic (Dirk, Whirl, Vesola) StephChars (Skip, Jana, Kou) Gemma Nasya Wido Flame Ivory Willo Feels HorizonChars (Milne, Iclyn) Silverhorn (Aether, Inazuma) Cacee "Kiwi" Cactus Piroli the Butterfly The Derp Wheelchair Inazuma

Multiplayer

Not needed unless hosting or playing singleplayer/locally.

Modes

SRB2 Battle! (BattleMod) Chaos Mode Pizza Time (Alternate take)

Exe Survival and Exe Terrorism come with Sonic.EXE (above).

Gameplay

Coop or Die! The Special Minigames

Maps

Mercenary Pack The Chaos Jam

Total conversion that turns the game into an FPS with a new campaign

Character: Samus Aran
Multiplayer: Hunters

The ultimate racing crossover

Mod Link Server Browser

Utilities

Nyoom Launcher for quick mod loading. Jeck Jims' SRB2Kart 3D DLC, and Community Models are also suggested. Player Bot Mod is an alternative to joining online.

Alternate Builds

SRB2Kart Galaxy for FPS boost, better character select, camera tilting, and server browser quick join support. Sonic Kart VR Mod adds what it says.

No addons are really needed unless you want to host you own server. Or to play them in singleplayer/locally.

Maps

Kart Rev Masters Pack Nightmare Pack Abstraction Pack Chengi's Track Attack Pack Aparte Cup Slipgate Cup

Tweaks

KartMP Juicebox Hitfeed Driftboost Gauge HORNMOD

Gameplay

Chaos Drives Wipezones Team SRB2Kart Racing FRIENDMOD Paragliders ChaosKart Elimination Weathermod Battle Plus

The ring-charged, unlock-packed sequel

Main Site Server Browser

It's a JRPG with multiplayer now

Mod Link

Some characters have Persona support.

Now it's like an MMO in the style of Phantasy Star Portable 2 Infinity. Complete with Symbol Art.

Mod Link (Or just join a server)

Make

Zone Builder to make maps. Lua for scripting.

Find More

The forum hosts all the addons, sorted by top and featured.

Background taken from official site.

Suggest more in the comments!