Botsociety - Botsociety is a tool to design, preview and export your chatbot.
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Balsamiq Mockups 3 - New public beta for the popular prototyping tool
Invision - Prototyping and collaboration for design teams
Bots UI Kit - Fully customizable Sketch UI Kit for Messenger Platform
Sketch - Professional digital design for Mac.