Balsamiq is a wireframing and prototyping tool that allows users to quickly create low-fidelity mockups of websites and apps. It has a simple drag-and-drop interface with pre-made widgets and icons to build screen designs. The desktop version runs on Windows, Mac, Linux, iOS, and Android, and it can export designs as PNG or PDF files. Balsamiq is intended for rapid prototyping early in the design process to visualize and share ideas with teams.