Nitrux
An icon theme for Linux.
https://github.com/Nitrux/nitrux-icon-theme
Icons are licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Nitrux was initially released in 2012. Nitrux provides simple and beautiful monochromatic icons for the UI for use in toolbars, menus, buttons, etc. and square-shaped icons for the applications.