Download of FLUID UI 1.1.1 for Mac was available from the developer's website when we last checked. We cannot confirm if there is a free download of this app available. We recommend checking the downloaded files with any free antivirus. This free software for Mac OS X was originally designed by Fluid Software Ltd. The application lies within Internet & Network Tools, more precisely Browser extensions.
From the developer:
Fluid UI is a browser extension mobile app prototyping tool. As with all creative tools, you start with a blank canvas. Simply double click to create a page. Within the page settings select the device you are prototyping to change the page size or choose the custom option to input your own dimensions. Currently supports iPhone, iPad, Android, Android tablet and Windows 8.
You may want to check out more Mac applications, such as Fluid Pressure and Flow, Fluid Noise Generator or UI Browser, which might be similar to FLUID UI.