Circle-style and minimalist icons
Vimix Theme
Vimix is a flat Material Design theme for GTK 3, GTK 2 and Gnome-Shell which supports GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon, XFCE, Mate, etc.
Matcha Theme
Matcha is a flat Design theme for GTK 3, GTK 2 and Gnome-Shell which supports GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon, XFCE, Mate, etc.
EvoPop Theme
EvoPop is a modern desktop theme suite.
Zafiro Icons
Minimalist icons created with the flat-desing technique, utilizing washed out colors and always accompanied by white.
Paper Icons
Paper is a modern freedesktop icon theme whose design is based around the use of bold colours and simple geometric shapes to compose icons.
Ikon Papirus
Papirus is a free and open source SVG icon theme for Linux, based on Paper Icon Set with a lot of new icons and a few extras, like Hardcode-Tray support, KDE colorscheme support, Folder Color support, and others.
Flat Remix Icons
Flat Remix ICON theme is a pretty simple Linux icon theme inspired on material design.