Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Craftwork - A collection of User Interface resources made by Craftwork
Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
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.
Invision - Prototyping and collaboration for design teams