fluidIA is described as 'FluidIA is an emerging agile design tool for prototyping rich user interfaces. This web based tool allows for rapid refinement and exploration of concepts using an object-oriented approach to design'. There are more than 25 alternatives to fluidIA, not only websites but also apps for a variety of platforms, including Windows, Mac, iPad and iPhone. The best alternative is Pencil Project, which is both free and Open Source. Other great sites and apps similar to fluidIA are Microsoft Office Visio (Paid), Lucidchart (Freemium), OmniGraffle (Paid) and Wondershare EdrawMax (Paid).
Microsoft Office Visio makes it easy for IT and business professionals to visualize, explore, and communicate complex information. Go from complicated text and tables that are hard to understand to Visio diagrams that communicate information at a glance.
Lucidchart is a visual workspace that combines diagramming, collaboration, and data visualization to accelerate understanding and drive innovation. With this intuitive, cloud-based solution, everyone can work visually and collaborate in real time.
OmniGraffle can help you make eye-popping graphic documents—quickly—by providing powerful styling tools, keeping lines connected to shapes even when they’re moved, and magically organizing diagrams with just one click.