JustVector Social Icons 1.0
alexpeattie.com/projects/justvector_icons
From the page
Saved with the link. Notes from 2007 to 2016 are mostly the page's own words, so this is probably an excerpt.
These 100 monochrome social icons are designed with simplicity in mind. Provided in vector format, they are fully editable and scale smoothly. They are completely free, even for commercial use, redistribution or remixing (see License).