Responsify – Web-Based Responsive Grid Template Generator
Responsify is a free, web-based application for creating a totally customized responsive base for a web project.
The project doesn't force us to use pre-defined number of columns or gutter-width but allows us to build the grid we want.
We can add any number of breakpoints and, also, live-preview how the template behaves on each width.
Once the template is ready, it can be downloaded as a .zip file which includes a PNG grid (for prototyping) besides the HTML-CSS files.