Snow appSnow is Theming tool that is open source under the GPL-3.0-only license. 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.
Submitting icon requests helps a lot, but maintaining the project (as you may imagine) takes a lot of time and effort, so please be patient about adding new icons. Contributions for new icons are always welcome, and no experience with programming is necessary.