Fluid UI is a browser-based wireframing and prototyping tool developed by Fluid Software and used to design mobile touch interfaces.
License: Freemium
Axure RP is a powerful tool ideal for complex prototypes with detailed interactivity and user testing features, making it suitable for larger projects. In contrast, Fluid UI offers a more user-friendly interface and is better for quick, collaborative prototyping, but lacks some of the advanced features found in Axure.