Papirus suite is specifically designed for KDE desktop but now the icon theme is available for other desktops as well which includes: Unity, Gnome, Mate, Cinnamon and others. Previously we had a ported version of Papirus KDE icons in the PPA but now it is directly supported and maintained by creator. There are two variants in this icon pack with light and dark panel icons, it has more than 3500 icons for different applications and still counting, if you find any missing icon then directly report it creator via Github page. There was an official PPA but discontinued back in November 2016 and now these icons can be installed via wget method. You can use Unity Tweak Tool, Gnome-tweak-tool to change themes/icons.