When I found out 343 was porting maps from fileshares to MCC fileshares, I made sure I saved as many good gametypes and maps as I could. I knew most maps like dig to china and jenga would be saved by hundreds of people so I ignored those, and instead looked on ForgeHub's Halo 3 archives to try and find a lot of really good maps that people may not have thought to save. I've also included a few maps and gametypes I made that are more meh because I intended to improve them. 

Map: The other side
Gametype: I hear it's safe
Description: "I hear it's safe on the other side" is a linear infeciton map where humans have to move through a multi-level parking garage and across the street to try and reach safety in a factory.

Map: UNSC Holdout
Gametype: Covie Assault
Description: Humans take the role of marines in a massive base with a large amount of weapons and vehicles facing a near unending assault of of infected covenant. Being marines, their health doesn't recharge and they must use medkits (custom powerups) scattered around the map to heal themselves. The last man standing becomes a spartan, stronger than the marines and able to recharge their shields.

Map: Z-War
Gametype: Z-War
Description: Humans spawn scattered across a map on sandbox with the towers turned off. They need to scavenge for weapons and equipment while avoiding zombies. Vehicles are helpful but require gas (custom powerups) to use. The zombies are heavily resistant to damage aside from headshots, but after about 90 seconds start to slow down in speed. At about 3 minutes in night falls in the desert and only the city in the center of the map as long as a few small outposts have the light needed.

Map: Z Survival
Gametype: Z-War
Description: Pretty much Z-War but slightly different

Map: HC Slayer
Gametype: HC Slayer
Description: up to 4 teams of 4 spawn in bases across sandbox. They have one life, 5 rounds and headshots are instant kill, but health is only slightly buffed. teams change bases every round

Map: Uno
Gametype: No custom mode. Just do infection but make the zombies white with poor camo.
Description: This one is a bit of a goof map that I saved because whoever made it put a ton of work into it, and it's pretty funny still. You need to see it to really get it.

Map: Romero Zombies
Gametype: Romero Zombies 
Description: Like night of the living dead, survivors hold out in a house against slow moving headshot only zombies. The building has multiple entrances that gain and lose accessibility as the match goes on

Map: Air Raid
Gametype: Any team mode
Description: Two massive ships float over Avalanche. One is an air craft carrier sporting banshees and hornets. The other is a type of battleship with a lot of turrets and more detailed inside. Works well for team modes of all types, especially asymmetrical ones

Map: Yublarin virus
Gametype: Infection
Description: a well forged infection map. 

Map: Human Resources
Gametype: A fire in
Description: A close quarters linear infection map where the humans have to move out of a burning office building

Map: Reach
Gametype: Covenant invasion
Description: A massive covenant cruiser sits above Reach dropping covenant (zombies). Watch out for the golden shipmaster

Map: Digamma City
Gametype: name slips my mind. Use the gametype by the dude with the same name as the map's maker. I'll update this soon
Description: Another tight quarters infection map in a dense city. There are plenty of places to hide and run through. watch out for the op red zombie

Map: Black Chapel
Gametype: Virus Strain 57
Description: Humans have to hold out in a church as the infected they fight gain more and more avenues of attack through spawning lifts and shield doors. That isn't to say it's hopeless, as time goes on the humans gain access to more and more caches of weapons, which are desperately needed as their ammo is limited. Teamwork is essential for winning for both sides.

Map: Rooftops
Gametype: Virus Strain 57
Description: Another in a great series of maps designed around the idea of a balanced infection game where both sides use a constantly changing map to their advantage. this one takes place on a series of rooftops

Map: Theactrical
Gametype: Virus Strain 57
Description: Another map in the Virus Strain 57 series, this one is set in an abandoned theater

Map: Final Stop
Gametype: Asset v2
Description: Remember that mission in ODST where you have to escort the engineer and when you were near him you had overshields? This gamemode works like that. One team is ODSTs escorting their Engineer VIP past covenant forces to a hornet that will spawn and take them to their extraction point. On this map, the ODSTs have to move through a train station.

Map: Ridgeline
Gametype: Asset v2
Description: Like the last map, the ODSTs have to protect their Engineer. This time, they have a bit more room to breathe, but also more ways to be attacked.

Map: Protocol
Gametype: Asset v2
Description: Another Asset map. 

Map: Soul Asylum
Gametype: DOOM
Description: In this mode the humans have to watch their back and navigate through a dark maze as they're hunted by an invisible predator who wields a sword and a laser. Teamwork is essential as wandering off just leads to people getting picked off. One of the coolest aspects of this map is that the maze actually changes every round. Some paths close and others open up. 

Map: Lubumba District
Gametype: ODST Infection
Description: Another map made during the ODST fever, the humans play as ODSTs fighting a variety of covenant infected. This map utilized a lot of clever features such as custom powerups acting as health kits to recharge an ODST's stalled healthbar, and a class system for the covenant made with tunnels they drop into

Map: Scarface
Gametype: Tony Montana
Description: The last man standing plays as Tony Montana fighting off an endless stream of hitmen in a faithful recreation of Tony Montana's house in the final scenes of Scar Face. 

Map: The City v3
Gametype: True Zombies
Description: A fun but difficult map where humans have 2 minutes to scavenge for weapons hidden all across a city and find buildings to hold up in before zombies fall from the sky at them. Nearly every building has multiple entrances and close sight-lines to make camping difficult to pull off without solid team work, just make sure you all have enough ammo before the zombies are released.

Map: Sandheart Manor
Gametype: Standard infection modes
Description: A massive mansion built into the giant dune on sandbox is even more impressive when you realize how much of a pain merging all the blocks must've been. This labyrinthine manor has a ton of rooms and close quarters to make survival a fun, but difficult objective to achieve.

Map: Close the Door
Gametype: Works best for fatkid (gamemode coming)
Description: On Highground humans have a small base to hold up in with doors that can be closed and opened with melee hits. Make sure you guard the multiple entrances as fat kids try to break their way in and eat you. 

 Installation:
1) Download and extract the file
2) C:\Users\USER NAME\AppData\LocalLow\MCC\LocalFiles\STRING OF NUMBERS\Halo3
3) Place folders

If you like these customs but don't have people to play them with, feel free to join my discord. We have regular gamenights and plenty of people that play Halo all the time. Discord Link