Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Ouch! Illustrations by Icons8 - Professional, perfectly matching, and customizable illustrations for any designs
Craftwork - A collection of User Interface resources made by Craftwork
Control Illustrations - 108 free flat illustrations with customizable characters
Streamline - Streamline is a web-based vacation rental software that manages vacation rental properties with flipkey integration, online booking, lead management, credit card processing, etc.
Humaaans - Mix-&-match illustrations of humans with a design library.