IconStore - Free icon packs by first-class designers
Invision - Prototyping and collaboration for design teams
Streamline icons - The world’s largest icon pack library - 100k icons and illustrations.
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Feather Icons - Simply beautiful open source icons
Craftwork - A collection of User Interface resources made by Craftwork