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!
For all the PC stuff, I'm assuming you're using Windows 10-11 (some stuff works with 8 too), other OSes I know nothing about. (if something doesn't work for 11, make it look closer to 10 with ExplorerPatcher)
Also everything PC related benefits from poking around Winaero Tweaker, it has Old Shortcut Icons, Windows 7 Photo Viewer, and a few more things worth looking at.
Pre-XP:
Project 2k (modded Windows 10)
simpleclassictheme (Titlebar)
RetroBar (Taskbar)
OpenShell (Start Menu)
Classic Task Manager (applies to literally everything before windows 10)
Windows XP:
Legacy Update (for Windows XP)
Windows eXPerience (modded Windows 10)xfce-winxp-tc (themes, cursors, sounds, applications, and shell for xfce)
XPQ4 (windows XP linux distro)
WindowBlinds (cost money, comes with a free trial. XP theme)
Luna10 (free alternative)
XP Theme (free alternative)
RetroBar (Taskbar)
OpenShell (Start Menu)
VLC Skins (Authentic Media Player/General XP Skin)
Windows Media Player 8 skin for Windows Media Player 12
SpaceCadetPinball decomp (3D Space Pinball)
Classic Quicktime Player VLC Skin
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. Themeing guide here)
Vista/7:
Extended Kernal (lets modern apps work on Vista)
Windows 10to7 (modded Windows 10)
Vista R2 22H2 V7 (modded Windows 10)
revert8plus (windows 7 transformation pack for win 8-11)
Windows 8 To 7 Transformation Pack (windows 7 transformation pack for windows 8.x)
Windows 10(1809) to 7 Transformation Pack (windows 7 transformation pack for windows 10 1809)
MondySpartan's Windows 10 to Vista Guide
WindowBlinds (cost money, comes with a free trial) (Vista/7)
Glass8 (WindowBlinds alternative for Windows 8/Windows 10)
DWMBlurGlass (Glass8/WindowBlinds alternative for Windows 10/Windows 11)
BasicThemer5 (free alternative, kind of buggy)
StartIsBack (cost money, perfect 7 taskbar for 8/10, incompatible with WindowBlinds)
StartAllBack (cost money, same thing as StartIsBack but for 11, incompatible with WindowBlinds)
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
Windows Vista Sidebar for windows 8, 10, & 11 (8GadgetPack alternative)
Inkball (missing from the link above)
Windows 8/8.1:
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)
Phones:
OldOS (old iPhone theme, technically an app)
Nova Launcher (not old inherently, needs themed)
Holo Launcher (old Android launcher)
Android 4.0, 4.1 and 4.4 icons
Other:
system.css (design system for very old Mac systems)
Retroactive (older versions of various Mac programs)
NsCDE (90s desktop environment)
CDE (90s desktop environment)
RetroCoolTerm (retro terminal theme for linux)
Human theme (old Ubuntu Human theme for GTK)
DS theme for 3DS (if the visuals are broken, find another one, make sure to keep the music from this one) (3DS needs to be hacked)
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) (guide to find it here)
Original XBOX Legacy theme for Series X
XBOX 360 Blades theme for Series X and Xbox One
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)
MyPal (based on Firefox Quantum, 3.0 theme)
OtterBrowser (opera)
Redmond-Firefox (IE 6-8 theme for firefox)
MSFX (IE 5 theme for firefox)
eXPeriencefox (actually good IE 6 theme)
07fox (actually good IE 7 theme)
Aerofox8 (actually good IE 8 theme, currently read only but you can still download it and it still works, for now)
rinFox (IE 7 and 8 theme for firefox)
BeautyFox (IE 9, 10 and 11 theme for firefox)
Basilisk (looks like chrome/firefox)
Silverfox (chrome 2012 theme for firefox)
360chrome (without the spyware. old chrome theme)
ChromifyVivaldi (chrome 49 theme for Vivaldi)
Classic Blue Theme (back to 50) (old chrome colors)
Borealis (Netscape 5, I think??)
K-Meleon (Mozilla's Gecko layout)
SeaMonkey (made with old Firefox source code)
Retrozilla (old Firefox, designed for the Classic style)