Android Nougat GUI - Free fully customizable Android UI Kit for Sketch
Humaaans - Mix-&-match illustrations of humans with a design library.
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
DrawKit - MIT licensed SVG illustrations, in 2 styles
Epic Pxls - UI kits, icons, templates, mockups and more, free
Handsome Illustrations - Create unique illustrations for websites & applications.