Hi! Two things!
1: I'm taking suggestions, I love suggestions!
2: please do not use Stylish, if they don't let you download with Stylus, push the "Install style as userscript" button at the bottom, Stylish was stealing information a few years back, and is also really old, just FYI.
REQUIREMENTS:
Stylus (chrome, firefox, pale-moon alternative)
AND
Tampermonkey
OR
the pale-moon alternative
YOUTUBE:
websites:
Vidbit (2009 frontend (kind of), will have more stuff later)
Yoretude (2005, will change with time if they don't go down first)
Vidlii (awful, but the only one that I'm sure will never ever die)
Cleantalk (2005 frontend)
themes:
Cosmic Cat (previously "Ciulin's Youtube") (Cosmic Panda)
Youtube Redux (chrome, firefox)
youtube 2010
youtube 2010-2011 html5 video player
OR
classic youtube player
7kttube (2016)
functionality:
Youtube Right Side Description
Youtube Proper Description
Youtube shorts redirect
Recreate old YouTube Footer!
TWITTER:
websites:
Good Ol' Twitter (2011 frontend, comes with app for iOS)
Bwitter (2007)
Blips.club (better version of bwitter) (NO LONGER! it is now 2009)
themes:
GoodTwitter2 (2016)
2020 - Twitter 2013 style (guess)
functionality:
De-rounding twitter
Twitter 16MODES Theme (DIM) (download the Bwitter background and use that)
Reigning in the new Twitter UI
REDDIT:
any "reddit to old reddit" extension or script
AND
Classic Reddit
AND
Old Snoo
ROBLOX:
themes (because i refuse to talk about revivals):
Roblox 2007 {READ DESCRIPTION IMPORTANT} (really bad)
Roblox, but everything is in Comic Sans (use this instead of the comic sans they suggest)
Roblox 2008 look (requires BTRoblox and some settings I don't remember (they're on one of the other pages), sometimes it breaks but it fixes itself with a refresh)
Roblox 2010 style (this one has the BTRoblox settings)
Roblox 2008-2011 theme (2008, 2009, 2010, 2011)
ROBLOX 2012
Roblox 2014
ROBLOX 2016 - a theme to mimic 2016
ROBLOX 2016 Avatar Editor Reconstruct
ROBLOX 2016 Sign Up Page Reconstruct (Read Desc)
Old Roblox Font (SourceSansPro)
2011 Roblox Blog (despite saying 2011, the look also works for 2010-2007 because they didn't change the design until later)
the game:
Google Drive full of mods (no scripts, just visual changes, open the RobloxPlayer file location and put all the files there, replace the files that are already there)
AND
guide to fixing the annoying roblox app (I have no idea if this is still an issue. windows only)
GOOGLE:
themes:
2018 Google
Google 2009 layout (Fixed)
Google search "old style"
websites
oldgoogle (1998, 2009, 2010, 2011, 2013)
Foogle (2016??? i think?? i dont remember)
STEAM:
Steam in 2007
AND
OG-Steam (2007, the rest of the steam links are skins and this is the only one i tested)
Old Steam skin 2010
Steam 2013
AND
2013 inspired steam library
AND
2010 Inspired Steam Friends (2010 steam friends, untested)
MISC THEMES/WEBSITES/SERVICES:
Spacehey (you're here!)
theretrobook (Facebook)
Newgrounds 2004
AND
Newgrounds - Pico & Friends Voting Icons (you only need the Pico icons)
AND
RemoveSupporterPfp
oldyahoo (Yahoo, 2012 and 2013)
SkeuoCord (Discord)
OR
DTM-08 (Basically the same as SkeuoCord, except this one has round PFPs)
DTM-16 (Discord 2016)
Ripcord (alternative discord/slack client, looks more "old web" to me)
Escargot (MSN)
Nina (Q-Link, Classic AOL, AOL IM, ICQ (whatever that is), and Yahoo Messenger)
Pheonix (looks like it does the same thing as Nina, except maybe people actually use this one)
Neocities (Geocities)
RiiConnect24 (Wii WIFI)
Wiimmfi (Wii and DS WIFI)
Sudomemo (Flipnote Hatena)
Ruffle (Flash Emulator for browsers, does not work with Yoretude for some reason)
Flash Projector (for the stuff that ruffle wont play)
Toontown Rewritten (old toontown)
Old School RuneScape (It's still going!)
New Club Penguin (no idea if this will last or if its popular, but there will always be a Club Penguin revival somewhere)
InsaneJournal (livejournal)
Dreamwidth (livejournal)
My 2000's TV! (2000s TV, goes all the way back to the 60s)
Toonami Aftermath (same concept, just Toonami)
Old Scratch (doesn't really have a name)
literally every other website:
Redirector (chrome, firefox, pale-moon alternative)
AND
OR
Wayback Machine - toolbar toggler
Wayback Machine Image Fixer
AND
Favicon Switcher (chrome, firefox, pale-moon users get nothing)
AND
Logopedia
(also CloudConvert to turn those PNGs into ICOs for things like shortcuts, if you need to)
Sorry for the weird formatting, no idea what happened. Thanks for reading, I'll keep this post updated with both my and your findings