8/14/20 update:

Maps Added:
Aperture Science Innovators by r101stairborne
Europa by logical
Leviathan by Jbird632 and co.
Nuketown Zombies by Clix
Sorry! Zombies by KillJoy

Mods Added:
Reaps BO4 Perk mod by F3ARxReaper666

3/29/20 update:

Maps Added:
Area 51 by steviewonder87

9/22/19 update:

Mods Added:
Boss Rush by Korlesa

7/27/19 update:

Maps Added:
Blood Run: Tranzit by Spiki
Little Garden Zombies by xdferpc

5/28/19 update:

Mods Added:
Mob of the Dead Remastered Patch by MotoLegacy (god bless this mod)

Maps Added:
Khufu's Revenge! by logical

5/13/19 update:

Mods Added:
Roll the Dice Mod by JeffSkye

MP maps added:
Warhawk by robit

Zombies maps added:
American Sniper by ZRK
Fabrik Der Untoten by Madgazgaming
Octagonal Ascension by I haZzZ RabieZ
Pharaoh's Curse by Player
Pinaka Tou Diavolou by SpIdeR
Private Property Extended by #xoxo r4d
The Last Crusade by Symbo

5/6/19 update part 2:
Mods Added:
Fun Mode (Exo Movement Version) by Collie

Maps Added:
Ah-Peku by Zindea (note: almost all Zindea maps would be on this collection, amazing map maker)
Blackwoods by Marksman147
Bunbury Redux by Ping998
Emergence by GalacticVerge
House, Facility, Temple, Overlook (DS map remakes) by MCDC101
Mori by eMoX MaNgA
Project Solitude by Rhys1201
Shi Koku, Japanese Tower by Killjoy (same as with Zindea, check out Killjoy's stuff, all great)
Shisha No Teikou by dadakhr
Town of Sorrow by Awesome Pie Man
Town Remastered by Slayin
Twisted Minds by IceGrenade (IceGrenade is the man to go to for challenging maps)

5/6/19 update:
Maps added:
Dead Ship by ZCTxCHAOSx
Bleakfalls by ProfessorWeeWoo
Dakhma by Joe M.
Dome by I haZzZ RabieZ
Frigid by Steviewonder87
Operation Loucher by MadgazGaming
Return to Das Herrenhaus by Seth Norris
Pieman's Christmas map remastered by McCall
Tiny Christmas by BluEShark
Wanted by ZeRoY

Note: I do not add in all the maps I think are good. Most maps are worth playing (besides most box maps and first room challenges, like come on guys there are 100s of maps incredibly similar to yours), and i can only add maps i am currently subbed to, meaning some get missed out.