Snow

Snow is a simple monocolored icon pack forked from Frost. Snow is FOSS and provides mostly icons for open-source apps on F-Droid (but there are many other apps in this pack too). The design is aiming to be simple with easy recognisable shapes.

Snow includes support for a lot of launchers like Trebuchet, KISS, Nova, Apex, Holo, ZenUI, ADW, and many more. The installation depends on your launcher, it's probably somewhere in the settings.