CoSketch - CoSketch is a multi-user online whiteboard designed to give you the ability to quickly visualize and share your ideas as images. No registration or plugins required.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Coccinella - Coccinella is a free and open-source cross-platform instant messaging client with a built-in...
Invision - Prototyping and collaboration for design teams
Conceptboard - Instant Whiteboards for Teams & Projects
Sketch - Professional digital design for Mac.