Adobe Edge Reflow CC is available as part of Adobe Creative Cloud for as little as $19.99/month.

Edge Reflow CC enables designers to build beautiful responsive web designs. Create on a native web surface with CSS design and layout features in a familiar and intuitive way. Preview and share your designs on-device through the integrated Edge Inspect plugin. Communicate your website's responsive behavior and intent, ensuring your design vision isn't compromised.

Version 0.23:

• Flexible design approach
• Text Styling
• Visual media-query breakpoints
• Improved Layout
• Smart guides & fluid grid system
• Asset management
• CSS Styling
• Preview
• Sharing

Requirements

• OS X 10.6 or later
• 1GB of RAM
• 200MB of available hard-disk space for installation
• 1280x800 display with 16-bit video card