Thought of this for a while, even if some stuff here is known to a degree.
- Most Doom/id based phone games, specially Resurrection https://www.youtube.com/watch?v=m8KoU_z9MOM and the BREW version of Doom RPG 1 https://www.youtube.com/watch?v=K_0U09e5SHk
- There's like 4 known versions of Doom 4: The Call of Doom one is obvious, the CroTeam version https://cdn.discordapp.com/attachments/217838275245637632/238740557608910848/seriousdoom.jpg and a version of 2016 that was said to star a cybernetic marine https://www.youtube.com/watch?v=5-vtXZT8Y_c possibly before the Night Sentinel were a thing in current Doom lore.
- The Doom 64 sequel https://lostmediawiki.com/Doom_Absolution_(lost_build_of_cancelled_Nintendo_64_sequel_to_%22Doom_64%22;_1997)
- Official UAC site that used Flash and had UAC related lore, mostly related to the Doom 3 novels or Doom RPG https://web.archive.org/web/20040716034658/http://www.ua-corp.com/ and https://web.archive.org/web/20051230053734/http://www.doomrpg.com/n.x/UAC/Home And Also https://doomwiki.org/wiki/Ian_Kelliher
- There's potentially more unused Doom 1/2 content that has yet to come out before ZeniMax forbid Romero from releasing more of it https://www.doomworld.com/forum/topic/119510-sad-news-on-new-unreleased-content/
- Unofficial Hungarian Doom books https://www.doomworld.com/forum/topic/98105-hungarian-doom-novels/
- A fanmade Doom comic from an old gaming magazine https://twitter.com/SarkSweet/status/1114638294367780867 and https://twitter.com/SarkSweet/status/1447150777806508034 It's in Greek.
- Obscure ports like WebTV Plus and Tapwave Zodiac, you can find these on the Doomwiki.
- The Cancelled 90's Doom movie, with concept artwork of demon models https://twitter.com/HDoomguy/status/1298008268015579136 and https://twitter.com/SlappyCromwell/status/1293063549686865920
- An obscure piece of merchandise being a snowboard with unique artwork, called "The Forgotten Son of Phobos", wonder who the artist is https://static.doomworld.com/monthly_2020_08/1704387035_forgottensnowboardofdoom.jpg.1d095d9c1500b093541edf5b378a7c9f.jpg
- Some old wads like Memento Mori having infopacks https://doomwiki.org/wiki/Memento_Mori#Infopack
- I think everyone knows about the Doom 3DO FMV photos already.
- Known cancelled/lost wads like Doom X https://www.doomx.net/
- Lost maps and music tracks from DWANGO https://www.youtube.com/watch?v=RXGtCjdwwe8
- The texts made for Doom 2's Master Levels https://doomwiki.org/wiki/DOOM-IT
- Recently discovered easter eggs in Sega Saturn Doom https://www.youtube.com/watch?v=NMHrbuYANZE
- Doomguy's cameo in this secret film, available in Quake's Saturn version https://www.youtube.com/watch?v=O4lCaLsoYxg
- Windows 98 Doom screen savers https://www.youtube.com/watch?v=j6ePnsB41GI
- Maybe wads that some id devs made outside of official Doom levels like https://doomwiki.org/wiki/Id_Map01 and https://www.doomworld.com/idgames/levels/doom/j-l/kickdm
I wonder if anyone else has any ideas or suggestions.
This sounds like it would serve for an iceberg template video or image.
If anyone ever makes a video or article of a topic like this, there are some people i think could do a good job at it (MarphyBlack, Decino, Doomkid, Dwars, Coincidente, Quasar of the Doomwiki, Kinsie, Linguica, probably more people i'm forgetting right now).