So you got your websites, but your computer still looks like it's chilling in 2024, what's worse is that all the devices around your computer ALSO still look freakishly modern, but I have themes to fix this!
Pre-XP:
Project 2k (modded Windows 10)
simpleclassictheme (free alternative)
Enable Classic Theme by handle method (free alternative) (transparency fix) (browsers fix) (maximized fix) (UWP fix) (list view fix)
RetroBar (Taskbar)
OpenShell (Start Menu)
Outlook Express 6.0 (98 Mail)
Hover! (classic 95 game)
Classic Windows Applications (98 CD Player, 98 Notepad, 98 Volume Mixer, 98 Wordpad, 98 Telnet)
Classic Windows Applications 2 (98 Games, 98 Wordpad, Writer, 98 Notepad, CD Player, Deluxe CD Player, 98 Sound Recorder, Mplay32, 98 Master Volume, 98 Telnet)
Windows Millennium Remote Control
Windows Movie Maker 1.0 (Windows ME)
wcecl (Windows CE apps on modern OSes)
Winevdm (16x apps on modern Windows)
Icons of Win16 apps in Explorer
Misc Windows (Assortment of Windows 1.01/2.03 applications)
Explorer 32px Icons (old Medium Icon size)
winfile (Windows 3.1 file manager)
Windows NT 3.1 Apps (Assortment of Windows 3.1 applications)
Windows 3.x Program Manager for Windows 7, 8, 8.1 and 10
Progman (3.x Program Manager recreation)
Windows NT 4.0's Welcome program
No Run Icon (removes the windows icon from the Run dialog box, like XP and earlier)
Chicago95 (Windows 95 theme for Linux)
B00merang-Project (1.0/2.0/3.11/95 theme for Linux)
Hotdog LINUX (Windows 3.1 Linux OS)
Chicago95 theme for LibreOffice (Windows 95 Word theme)
Windows XP:
Legacy Update (for Windows XP)
Windows eXPerience (modded Windows 10)WindowBlinds (cost money, comes with a free trial. XP theme)
Luna10 (free alternative)
XP Theme (free alternative)
RetroBar (Taskbar)
OpenShell (Start Menu)
Windows Media Player 8 skin for Windows Media Player 12
XP Photo Viewer (set it to be used by default)
Classic Desktop Icons (2000-XP icon select effect)
Classic Windows Applications (XP Sound Recorder, XP Volume Mixer, XP CD Player, XP End of Life Warning)
Classic Windows Applications 2 (XP DXDiag, XP End of Life Warning)
XP Open With (unstable, use with caution)
SpaceCadetPinball decomp (3D Space Pinball)
MSN-Explorer-Enabler (Reenables MSN Explorer 6/7)
Classic Quicktime Player VLC Skin
VLC Skins (Authentic Media Player/General XP Skin)
Windows Media Player 9 (bundled with XP SP2+)Windows Media Player Skins Archive (Windows 9x-XP media player skins)
FindeXer (file explorer, hard to download, requires running a bat file as admin in system32 to work, avoid if you can. Theming guide here)
Classic File Picker dialog (2000-XP)
Explorer 32px Icons (old Medium Icon size)
No Run Icon (removes the windows icon from the Run dialog box, like XP and earlier)
xfce-winxp-tc (themes, cursors, sounds, applications, and shell for XFCE)
RedmondXP (XP theme for GTK and XFCE)XPQ4 (Windows XP Linux distro)
B00merang-Project (XP/XP Classic theme for Linux)
Vista/7:
Extended Kernal (lets modern apps work on Vista)
Windows Vibranihorn RC 2.1 (modded Windows 10, looks like Vista)
Reloaded7 (modded Windows 10)
Classic 7 (modded Windows 10)
revert8plus (windows 7 transformation pack for win 8-11)
Windows 10(1809) to 7 Transformation Pack
Windows 10 (21H2-22H2) to 7 Transformation Pack
MondySpartan's Windows 10 to Vista Guide
WindowBlinds (cost money, comes with a free trial) (Vista/7)
BasicThemer6 (free alternative)
OpenGlass (Aero Glass alternative for Windows 8/Windows 11)
DWMBlurGlass (WindowBlinds alternative for Windows 10/Windows 11)
StartIsBack (cost money, 7 taskbar for 8/10, incompatible with WindowBlinds) (accuracy tweaks)
StartAllBack (cost money, same thing as StartIsBack but for 11, incompatible with WindowBlinds)
RetroBar (Taskbar, free alternative for Vista)
OpenShell (Start Menu, free alternative for Vista)
Windows Media Center 7/Vista (installBLUE.cmd for the blue themed version, choose installGREEN.cmd
for the green themed version. Blue is recommended if you're going for
accuracy because the Green version was only officially installable on
Windows 8/8.1. If you don't see it on your PC after you install it
restart your PC.) (thanks Quentin)
Windows Media Player 12 VLC Skin
8GadgetPack (Weather Gadget fix)
Windows Vista Sidebar for windows 8, 10, & 11 (8GadgetPack alternative)
Windows Vista/7 Gadgets (8GadgetPack alternative)
Windows Vista-exclusive gadgets for Windows 7 (works for 8GadgetPack)
Library Header For Windows 8+ (oldnewexplorer alternative)
Control Panel Restoration Pack
Inkball (missing from the link above)
Classic Wordpad (7-10)
Classic Notepad (7-10)
Restoring classic volume context menu options (Windows 7 Volume Control context menu)
WinFlip (Vista 3D Flip)
Vista Security Center and Firewall applets
Vista Tablet PC & Pen & Touch CPL
7/Vista Keyboard Layout Manager
Vista Network Activity Indicator
Microsoft SharePoint Designer 2010 and Microsoft Office Picture Manager
Open Live Writer (newer, open source version of Windows Live Writer 2012)
The Green Button (Windows Media Center theme for Kodi)
AEROTHEMEPLASMA (7 theme for KDE Plasma)
B00merang-Project (Vista/7 theme for GTK/GNOME)
Office 2013 theme for LibreOffice
Windows 8/8.1:
ProjectBlue (modded Windows 10, looks like 8.1)
Metro 10 v2 (modded Windows 10, looks like 8.1)
Windows 10x8 (modded Windows 10, looks like 8.0)
WindowBlinds (cost money, comes with a free trial) (8.x)
Aero10: Metro (free alternative)
Center Titlebar (titlebar like in win 8.x)
Windows 8 Start Screen Update + Download (requires Start11 in Windows 10 Style)
WinMetro (free alternative, must be set to windows 7 compatibility mode)
Control Panel Restoration Pack
Add Features (from 8.1)
Location Settings Control Panel (from 8.1)
Performance Information and Tools (from 8.0)
Restoring classic volume context menu options (Windows 8/8.1 Volume Control context menu)
Charms Bar Port (Windows 8 Charms Bar for Windows 10/11)
B00merang-Project (8/8.1 theme for GTK/GNOME)
Windows 10:
RevertSV (modded Windows 11)
ExplorerPatcher (taskbar for Windows 11, does not work on newer versions)
Windows 10 1511's Security and Maintenance Control Panel
Classic Display Settings (from 1511)
Restoring classic volume context menu options (10056 Volume Control context menu)
Legacy Search Bar (Search Bar from 1909 and earlier)
Disable rounded corners in Windows 11
B00merang-Project (Windows 10 theme for GTK/GNOME)
Mac:
MacProxy Plus (lets modern websites work on very old Mac systems)
system.css (design system for very old Mac systems)
OS (Old School) (cost money, Mac 1-4 theme)
AquaLickX (older Mac OS X UI elements for modern macOS)
Classic Mac OS Finder (for Windows)
Retroactive (older versions of various Mac programs)
Front-Row (restores partial Front Row functionally on Mac OS Lion/Mountain Lion)
macOSLucidaGrande (old font for modern Mac systems)
ViFind (Yosemite-Catalina Menu Bar for Windows)
Lickable Menu Bar (Mavericks/Catalina/Tiger Menu Bar for modern Mac systems)
cDock (cost money, old Mac dock, version for Apple Silicon)
Mac OS X Yosemite Rocketdock theme
iTunes-Experiment (iTunes 10 recreation, needs to be compiled from source)
WinLaunch (Mac Launchpad for Windows)
Leopard-Mavericks Photobooth for Windows
Mac OS X Tiger Front Row for Windows
Mac OS X Address Book and Fontbook for Windows
Mac OS X System Preferences for Windows
Mac OS X Parallels Desktop for Windows (move Parallels folder to C: drive for the best effect)
Mac OS X CD/DVD Burning App for Windows
mfslives (allows modern Mac systems to run MFS images and floppy disk)
Executor 2000 (allows modern Mac systems to run older Mac applications)
Platinum9 (Mac OS 9 theme for Linux)
StyleProject (QT4/QT5 theme for Linux)
Yosemite Gtk Theme (Yosemite theme for Linux)
B00merang-Project (Leopard/Mavericks/Cheetah/Catalina/Catalina Dark/Mac OS 9/Mac System 4 theme for GTK/GNOME)
Hotdog LINUX (Classic Mac OS/Aqua Mac OS Linux OS)
Phones:
OldOS (old iPhone theme, technically an app)
iOS 6 Simulator written in Swift (old iPhone theme, technically an app)
iOS 6 Full Theme (iOS 6 theme for modern iOS)
Ultimate iOS 6 Theme Setup Guide (iOS 6 theme for jailbroken iOS)
Checkmate, Store! (allows older iOS devices to download new apps)
Electimon's Repo (allows older iOS devices to download new apps)
AppSync Unified (allows iOS 5+ devices to downgrade apps)
MapsX (fixes iOS 6-7 Maps)
EarthX (fixes Google Earth on old iOS devices)
iTunesStoreX (fixes iTunes stores for old iOS devices)
StoreLayoutsFix (fixes iTunes layout issues on iOS 6)
Modern 6 SE (iOS 6 Icons, Sounds, Wallpapers)
Espier Screen Locker i6 (iOS 6 lock screen for Android)
Espier Screen Locker 7 Pro (iOS 7 lock screen for Android)
Espier Dialer i6 (iOS 6 dialer for Android)
Espier Dialer 7 Pro (iOS 7 dialer for Android)
Espier Control Center 7 Pro (iOS 7 control center for Android)
Espier Music Controller (iOS 6 music control for Android)
Espier Reminders (iOS 6 reminders for Android)
Espier Clock (iOS 6 clock for Android)
iPhony (iOS 6 keyboard/mail for Android)
iLauncher (iOS 6 theme for Android)
Launcher 10 (Windows Phone 10 theme for Android)
Metro UI Launcher 8.1 (Windows 8.1 Tablet theme for Android)
Groove Launcher (Windows Phone 8 theme for Android)
Retiled (Windows Phone 8.x theme for Linux phones)
Lynn Launcher (MeeGo 1.2 theme for Android)
Meeye, Classic MeeGo Icon Pack
Belle ui for Klwp/Kwgt (Symbian launcher for Android, requires KLWP or KWGT)
Donut Launcher 1.3 (Android 1.3 theme)
Launcher 4.4.2 (Android 4.4.2/KitKat theme)
Android 4.4.4 (KitKat) Launcher
Android 5.0 (Lollipop) Launcher
Android Lollipop theme for iOS
Launcher <3 (Android 7-11 theme)
Galaxy S Launcher (Samsung Galaxy Touch Wiz theme for Android)
Nova Launcher (Android launcher, not old inherently, needs themed)
Nokia 1280 Launcher (for Android)
Holo Launcher (old Android launcher)
Android 4.0, 4.1 and 4.4 icons
Honeycomb Clock (Android 3.x clock)
Ice Cream Sandwich Clock (Android 4.x clock)
Android 1.6 Donut Global Clock
Android 1.6 Official Example Games
Nexus Revamped (Nexus Live Wallpaper for newer Android phones)
Android 4.x Phase Beam Wallpaper
Android 4.x Black Hole Wallpaper
Home Screen Tips widget for modern Android
ReLiveWP (restores some functionality to Windows Phone 7/8)
Live Store (Windows Phone 8.1 store)
Windows Phone 7 Apps for Android
Install with Options (removes limit on old apps for Android)
Tango (allows new Android devices to run older apps)
J2ME-Loader (allows new Android devices to run older Java apps)
WPR (allows new Android devices to run older Windows Phone games)
touchHLE (allows new Android devices to run older iOS games)
EKA2L1 (allows Android devices to run Symbian OS/N-Gage apps)
Nofun (allows Android devices to run Mophun apps)
Mythras (allows Android devices to run Mythroad apps)
BREWEmulator (allows Android devices to run Mythroad apps)
HTC Sense Apps port for All Devices
Other:
DiskClick (old HDD clicking sounds)
MikeBonnell.com (1997-2004 Desktop Wallpapers)
Old Icons (assortment of old ICOs)
Version Spoof (Fakes the Windows Version reported to applications)
Classic context menu on Windows 11
Classic Task Manager (applies to literally everything before windows 10)
Windows Journal (various Windows OSes had this)
Winaero Tweaker (various tweaks for Windows 10/11, allows for Classic Shortcut Icons, Windows 7 Photo Viewer, etc.)
Eradicate Immersive Menus (restores various old context menu themes for Windows)
Classic Task Dialog Fix (makes the buttons in task dialogs taller like Windows 8.1 and earlier)
Old This PC Commands (forces some commands to use Control Panel instead of Settings, doesn't work on Windows 11)
NTVDMx64 (MS-DOS apps on modern Windows)
KDE on Windows (early KDE apps on Windows)
VAIO Gate Dock for any computer (VAIO Gate for non-VAIO computers)
2ine (allows Linux devices to run OS/2 applications)
NsCDE (90s desktop environment)
CDE (90s desktop environment)
RetroCoolTerm (retro terminal theme for Linux)
GNUstep (NeXTSTEP theme for Linux)
OneStepBack (NeXTSTEP theme for GTK)
Human theme (old Ubuntu Human theme for GTK)
B00merang-Project (old ChromeOS/Unity 7/Unity 8/Solaris 8/Solaris 9/BeOS/Human/Adwaita/Old Fuchsia theme/80s Terminal/OS/2 Warp 4 for GTK/GNOME)
Hotdog LINUX (Atari ST/Amiga Linux OS)
DSI theme for 3DS (1/2/3) (3DS needs to be hacked)
DS Splash Screen for 3DS (3DS needs to be hacked)
DSI Splash Screen for 3DS (3DS needs to be hacked)
Wii theme for Switch (Grey/Blue) (Switch needs to be hacked)
PS2 Legacy Theme for PS4 (cost money, very cheap)
PRENXE v2+ (Xbox 360 Blades theme for Freestyle Dashboard)
AuroraNXE (Xbox 360 NXE theme for Aurora)
Proto Dash (Blades/NXE/Kinect theme for Proto Stealth)
Original XBOX Legacy theme for Series X
XBOX 360 Blades theme for Series X and Xbox One
TetradUI (XBOX 360 Blades theme for Kodi)
DroidTV (Android TV 2014-2015 theme for Kodi)
Dos Terminal (MS-DOS theme for LaunchBox)
Famicom Beach (50-in-One NES theme for Pegasus)
Mini Consoles Theme - RetroSai Nostalgia - Form over Function (Xbox 360 Blades/Xbox 360 Metro/Xbox One/PS3/PS4/Wii/Wii U/Famicom Classic/NES Classic/SNES Classic/Switch theme for LaunchBox)
NESiCAxLive Theme (NESiCAxLive theme for LaunchBox)
New Pegasus Experience Theme (Xbox 360 NXE theme for Pegasus)
switchOS (Switch theme for Pegasus)
Modern (Switch theme for EmulationStation)
AltHome (2018-2020 webOS TV theme)
Browsers:
Echelon (Firefox 4-29 theme)
Zap's Cool Photon Theme (Firefox 87 theme)
Pale Moon (more visually accurate firefox. Themes (including Firefox 1.0, 2.0, 3.0, Chrome, Opera and Netscape 4), IE 9/10 theme, Netscape 8 theme)
MyPal (based on Firefox Quantum, 3.0 theme)
OtterBrowser (Opera 12.x)
Redmond-Firefox (IE 6-8 theme for Firefox)
MSFX (IE 5 theme for Firefox)
IE 5 Mac Skin, OSX Safari Skin (2 different Firefox themes)
eXPeriencefox (actually good IE 6 theme)
07fox (actually good IE 7 theme)
rinFox (IE 7 and 8 theme for Firefox)
BeautyFox (IE 9, 10 and 11 theme for Firefox)
Geckium (Chrome 1-6, 11, 21, 25, 47, 58 theme for Firefox)
Basilisk (looks like chrome/Firefox)
360chrome (without the spyware. old chrome theme)
ChromifyVivaldi (Chrome 49 theme for Vivaldi)
Classic Blue Theme (back to 50) (old Chrome colors)
Modoki-Firefox (Modern Modoki Netscape theme for Firefox)
K-Meleon (Mozilla's Gecko layout)
SeaMonkey (made with old Firefox source code)
Retrozilla (old Firefox, designed for the Classic style)
Safari-Experiment (Snow Leopard Safari, Mac only)
If I'm missing something, let me know and I'll add it!