Balsamiq

Balsamiq is a rapid wireframing tool that helps designers and product teams visualize ideas quickly. Its focus on low-fidelity mockups encourages collaboration, feedback, and iteration during the early stages of product design. 

Key Features:

• Drag-and-drop wireframe components

• Sketch-style low-fidelity visuals

• Collaboration and comment tools

• Cloud and desktop versions available

• Ideal for product managers, designers, and developers