UX Flow Wireframe Prototyping System - Create beautiful user flows prototypes for your next project
Open Peeps - A hand-drawn illustration library.
React Proto - React application design and prototyping tool
Control Illustrations - 108 free flat illustrations with customizable characters
Balsamiq Mockups 3 - New public beta for the popular prototyping tool
Craftwork - A collection of User Interface resources made by Craftwork