Classy icons crafted according to Microsoft guidelines. Available in PNG and SVG. Free for a link
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Feather Icons - Simply beautiful open source icons
Super Tiny Social Icons - Under 1KB each! Minuscule SVG logos!
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+500 Animated Icons by Lordicon - Animated lottie icons for unforgettable user experience
Flat Icons - 20,000 unique, customizable icons with free lifetime updates