Themes Collection for Ubuntu 18.10 Cosmic/18.04 Bionic/16.04 Xenial/14.04 Trusty/12.04 Precise/Linux Mint 19/18/17 (Unity, Gnome Shell, GTK3, GTK2, Xfce, Cinnamon)

Icons can be found here
Note: Old (Obsoleted) Ubuntu Versions: Themes and icons for Ubuntu 17.10/17.04/16.10/15.10/15.04/14.10/13.10/13.04/12.10/11.10/Linux Mint 16/15/14/12

Ubuntu 18.04 Bionic/18.10 Cosmic Themes

Macbuntu 18.04 Transformation Pack
Ultimate Dark and Maia Plane Theme
Canta Themes Matcha Themes
Qogir Themes Flat Remix Themes
Vimix Themes Stylish Themes
Sweet Themes Arrongin and Telinkrin Themes

Ubuntu 16.04 Xenial Themes

MacBuntu OS (MBuntu) Transformation Pack for Ubuntu 16.04 Xenial Xerus
Vivacious Color Themes Yosembiance Smooth
Ubuntu 8.04 Theme (GTK) Ambiance & Radiance Flat Colors (GTK)
Ambiance & Radiance Colors Suite (GTK) Paper Gtk Theme
Arc Themes(GTK) Ambiance Crunchy themes(GTK)
Ambiance Lime (GTK 3) Flatabulous theme
Dark Aurora (GTK + Gnome Shell) Windows 10 Themes(GTK + Cinnamon)
Vimix themes Pack(GTK + Gnome Shell) Chrome OS themes Pack(GTK + Gnome Shell)
Windows XP Pack Minwaita (Gnome)
Albatross (Gnome) Pop Theme (System76)
Mist Theme(Gnome Shell) Aurora Next & Aurora Nuevo
T4G-V2 (Gnome) Flat Remix (Gnome)
Maxim Theme (Gnome Shell) Zukitwo & Zukitre (Gtk + Gnome Shell)
Obsidian (Gtk + Gnome Shell) Ultimate Blue(Gtk + Gnome Shell)
Victory (Gtk) Ashes (Gnome Shell & Gtk)
Numix Theme (Gtk) Cobibird Theme (Gtk)

Ubuntu 14.04 Trusty Tahr Themes

Mac OS X (MacBuntu) Transformation Pack for Ubuntu 14.04 Trusty Tahr
Mindows (Windows) Transformation Pack for Ubuntu/Linux Mint

Trevilla (GTK 3) Delorean Dark theme (GTK)
GnomishDark theme (GTK 3) GnomishGray (GTK 3)
GnomishBeige (GTK 3) Numix Theme (Gtk)
Ambiance Dark (GTK) Evolve theme(GTK 3)
Zukitwo, Zukiwi, Zukitre (GTK 3) Vimix themes Pack(GTK)
Moka theme(GTK) Flattastic themes Pack(GTK)
E17Gtk theme(GTK) Flatts theme suite(GTK)
Orchis theme(GTK) Ambiance Crunchy themes(GTK)
Ambiance-Lime theme (GTK 3) Ambiance & Radiance Colors Suite (GTK 3)
Win themes & icons (GTK + Cinnamon) Ambiance Dark Red(Gtk)
YlmfOS - Win XP (Gtk + Cinnamon) Numix Bluish (Gtk + Xfce)
Mediterranean themes (Gtk + Xfce) Ambiance Grey (Gtk)
Zukitwo Dark (Gnome Shell & Cinnamon) CobiBird theme(GTK & Xfce)
Dorian theme(GTK 3) Gnome Cupertino (GTK & Gnome Shell)
Zen Suite (Xfce) Faience (Gtk + Gnome Shell)
Flattice & FlatBird (Gtk + Xfce) Cenodark & Cenozoic (Gtk)
Rave-X Colors (Gtk) Polar Night (Gtk)
Ambiance Blackout Colors (Gtk + Gnome Shell) Ambiance & Radiance (Gnome shell)
Sable Suite (GTK) Hackstation (GTK, Gnome Shell, Cinnamon, XFCE)
Royal-Gtk theme(GTK 3) Ambiance & Radiance Flat Colors (GTK 3)
StylishDark (GTK) Libra (GTK)
Ubuntu Touch (GTK) Lhun-Magol Dark Theme (GTK)
Azure Material Design Theme (GTK) Ambiance Dark Blue Theme (GTK)
Ceti & Vertex (GTK + Gnome Shell + Cinnamon) Zukitwo Dark Reloaded(GTK & Xfce)
ZorinOS themes(GTK + Cinnamon) Mist Theme(Gnome Shell)
Windows 10 Themes(GTK + Cinnamon) Dark Aurora (GTK + Gnome Shell)
Flat-Plat Themes(GTK + Gnome Shell) Papirus Suite(KDE)
Delorean Dark Unity Flatabulous theme
Moka Project Suite Paper theme Suite
Zukitwo & Zukitre (Gtk + Gnome Shell) Cobibird Theme (Gtk)

Ubuntu 12.04 Precise/Linux Mint 13 Themes (Gnome Shell 3.4.x/3.5.x/, GTK 3)

Mac OS X Lion Theme Version 2 for Ubuntu 12.04 Precise Pangolin
Mac OS X Lion Theme for Ubuntu 12.04 Precise Pangolin
Best Malys Themes + Icons for Ubuntu/Mint (Gtk + Gnome Shell)
Transparent Swar Red Unity Theme for Ubuntu 12.04 Precise
Transparent Swar Themes for Ubuntu 12.04/Linux Mint (GTK3)
Transparent Swar Black Base Themes for all Ubuntu/Mint (GTK3)
Best theme for for Ubuntu 12.04/Linux Mint

GTK Themes
Trevilla (GTK 3) Uncomplicated Themes(GTK 3)
Mediterranean Themes(GTK 3) Dorian theme(GTK 3)
Daylight & Adwaita-Elements Themes(GTK3) Simplex Theme(GTK 3)
Omg-Suite Theme(GTK 3) Leopard-Steel Theme(GTK 3)
Orion Theme(GTK 3) Royal-Linux Themes(GTK 3)
zonColor Theme(GTK 3) WOW-2 Theme(GTK 3)
Malys-Future Theme(GTK 3) BorderLine theme(GTK 3)
Salience theme(GTK 3) Dark-Mint theme(GTK 3)
Elementaryish theme(GTK 3) GtkDroid JellyBean theme(GTK 3)
Ambiance Dark theme(GTK 3) Elegant Eggplant theme(GTK 3)
Clearbird theme(GTK 3) FlatStudio theme(GTK 3)
Clearlooks-Phenix theme(GTK3) Faience theme(GTK 3)
Malys-Rought theme(GTK 3) ClearNIX theme(GTK 3)
Swar Light-Blue theme(GTK 3) GreyBird GTK theme(GTK 3)
Mac-X-Reloaded theme(GTK 3) BlackCity theme(GTK 3)
TLS Dark theme(GTK 3) Delorean theme (GTK 3)
Malys-Revolt theme(GTK 3) Malys-Inversio theme(GTK 3)
Malys-Futurebox theme(GTK 3) Zukitwo Primary Colors theme(Gtk 3)
Evolve Theme(GTK 3) Elementary Dark Theme(GTK 3)
Malys-Unisex Theme(GTK 3) Malys-Revolt Theme(GTK 3)
Awesome Theme with Icons(GTK 3) Malys-Unicolors themes(GTK 3)
AmbianceP theme set (GTK 3) CobiBird theme(GTK)
Elegant Brit theme Neptune (GTK 3)
Plus1 & Futura (GTK) Smoothly Light & Dark (GTK)
Linux Deepin theme (GTK) GnomishDark theme (GTK 3)
GnomishBeige (GTK 3) Ambiance DS Blue (GTK 3)
Numix (GTK 3) Ambiance Lime (GTK 3)
Zen Suite (GTK 3) Windows Theme (GTK 3)
Linux Mint theme(GTK 3) Moka theme(GTK)
ZorinOS themes(GTK) Orchis theme(GTK)
Ambiance & Radiance Colors Suite (GTK 3) Gnome Cupertino (GTK)
Ambiance Blackout Flat Colors (GTK + Gnome Shell) Paper theme Suite

Gnome Shell Themes
Royal-Linux Themes(Gnome Shell) zonColor Theme(Gnome Shell)
eOS theme(Gnome Shell) Malys Future theme(Gnome Shell)
Malys Rought theme(Gnome Shell) Elegance Colors theme(Gnome Shell)
Zukitwo Cupertino theme(Gnome Shell) Sombre Porcelaine theme(Gnome Shell)
myeOS theme(Gnome Shell) Frosted Glass theme(Gnome Shell)
Optimus Blue Inspiration theme(Gnome Shell) Gobilum Shell Dark theme(Gnome Shell)
Malys Orange theme(Gnome Shell) eOS Theme(Gnome Shell)
Malys-GlassArt Themes(Gnome Shell) DarkShine Theme(Gnome Shell)
Gtk + Gnome Shell Themes
Simplex Theme(GTK 3 + Gnome Shell) Omg-Suite Theme(GTK 3 + Gnome Shell)
Royal-Linux Themes(GTK 3+ Gnome Shell) zonColor Theme(GTK 3 + Gnome Shell)
reNIX theme(GTK 3 + Gnome Shell) Boje & BorderLine (GTK 3 + Gnome Shell)
Faience theme(GTK 3 and Gnome Shell) GnomishDark theme(GTK 3 + Gnome Shell)
Mintu theme(GTK 3 + Gnome Shell) Ambiance Crunchy themes(GTK)
Energreen theme(GTK 3 + Gnome Shell) GnomishGray(GTK 3 + Gnome Shell)
Opal Black & Blue(GTK 3 + Gnome Shell) Fusion Dark theme(GTK 3 + Gnome Shell)
Malys Future theme(GTK 3 + Gnome Shell) Linux Mint theme(GTK 3 + Gnome Shell)
Old-Steampunk theme(Gnome Shell + Gtk3) GnomishDark theme(Gnome Shell + Gtk3)
Zukini Theme(Gnome Shell + GTK 3) Zukitwo Theme(Gnome Shell + GTK 3)
Plus1 (GTK + Gnome Shell) Plane-Gtk3 (GTK + Gnome Shell)
Linux Deepin theme (GTK + Shell) GnomishBeige (GTK 3 + Gnome Shell)
Darkair & Blo (GTK + Gnome Shell) Gnome Cupertino (GTK & Gnome Shell)

Cinnamon Themes
Simplex Theme(Cinnamon) Royal-Linux Themes(Cinnamon)
zonColor Theme(Cinnamon) Dark-Mint theme(Cinnamon)
Tout theme(Cinnamon) Malys Future theme(Cinnamon)
Linux Mint theme(Cinnamon) Bigfoot Red & Blue themes
Plus1 (Cinnamon) Numix (Cinnamon)
Windows Theme (Cinnamon) ZorinOS theme(Cinnamon)

Emerald Themes
Emerald Manager and Themes

Icons for Ubuntu/Linux Mint

Malys Uniblue/Uniblack icon sets AwOken/kAwOken Icons for Ubuntu/Linux Mint
FS Icons for Ubuntu/Linux Mint NouveGnome Icons for Ubuntu/Mint
eOS Blue Icons for Ubuntu/Linux Mint Azenis Dark Icons for Ubuntu/Linux Mint
Malys Ex Icons for Ubuntu/Linux Mint ACYL Icons and Manager for Ubuntu/Mint
Darkenza Icons for Ubuntu/Linux Mint Linux Mint Icons for Ubuntu/Mint
Lubuntu-Box Icons for Ubuntu/Mint Mac-X-Reloaded Icons for Ubuntu/Mint
Mint-X Icons for Ubuntu/Linux Mint MeliaeSVG Icons for Ubuntu/Mint
ArtNet icons for Ubuntu/Linux Mint Piratunbu Icons for Ubuntu/Mint
Azenis Dark Green Icons for Ubuntu/Mint Blue Remix icons for Ubuntu/Mint
Matrilineare Icons for Ubuntu/Mint iNX Icons for Ubuntu/Linux Mint
zonColor Icons for Ubuntu/Linux Mint Royal-Linux Icons for Ubuntu/Linux Mint
Elementary Icons for Ubuntu/Linux Mint My-Humanity Icons for Ubuntu/Mint
Ubudao-Style Icons for Ubuntu/Mint Nitrux2, Nitrux Icons for Ubuntu/Mint
OSX-Nostalgie Icons for Ubuntu/Mint G-Xiria Icons for Ubuntu/Mint/Debian
Trevilla Icons for Ubuntu/Linux Mint Elementary Sky-Blue for Ubuntu/Mint
Colored-Plastic for Ubuntu/Mint Magical Light for Ubuntu/Mint
Numix-uTouch Icons High-Delight & Hi-Light icon sets
Snow Sabre icons iLinux icons for Ubuntu/Linux Mint
Moka & Faba icons Aery icons for Ubuntu/Linux Mint
Compass icons for Ubuntu/Linux Mint Faenza & Faience icon sets
MyElementary icons Buttonized icons
Buuf + Remix icons Ffw-Fast-Forward icons
ieOS7 icons Zorin OS icons
Windows icons Kawaiki icons
Potenza Icons for Ubuntu/Linux Mint Mylo Xylo icons
Square icon set Malys-Uniwhite icons
FlatWoken icon set Numix Icon Pack
Square Beam Icon Pack Win XP Icons
MintX Colors Icons Sphere Icons
Ravefinity Icons Deepin Icons
EleMint Icons Ursa Icons
Rave-X Colors Icons Dalisha Icons
Sigma Metro Icons Ghost Flat Icons
Emerald Icon theme Sovietec-OS Icon theme
Ultra-Flat Icons Smaragd Octal Icons
Octagon Icons Victory Icons
Evolvere Icons Vibrantly-Simple Icons
Humanity-Colors Icons Nitrux (Official PPA) Icons
Masalla Icons Vimix Icons
Vivacious Colors Icons Clarity Icons
Shadow Icons Xenlism WildFire Icons
Papirus Icons Vertex Icons
Uniform Icons Humanitary Icons
Vertrux Icons Lila-HD Icons
Revival Icons Antu Icons
Arc Icons Ardis Icons
Elementary-Add Icons Victory Icons (V2)
Vibrancy-Colors Icons Linux Dark Icons
Oranchelo Icons Obisidian-1 Icons
Just Colors Icons Xatane Icons
Numix White Icons Pop Icons (System76)
Perforated Edge Icons Flat Remix Icons
DamaDamas Icons Vamox Icons
Ubo Icons ArdoNet Icons
Ultimate Maia Icons Plane Icons
Matcha Icons Delft Icons