First of all Responsive design is art for creating web site that can target multiple devices. Smart phone prices are going down so people started using smart phones for browsing instead of desktop. Making Responsive design is not that easy. But fortunately we have number of free tool on internet. Here I am listing out such tools which can help you create responsive web design so easily.
Basically Head.js not meant for responsive webdesign. Head.js will be used to parallel script loading. By using this plug-in we can improve performance of webpage. The webpage load time will increased by 50% after i used it in one of my web site. I am listing it here because it has a great feature of supporting responsive design also. We just need to create classes like .lt-1024,.lt-980,so on.
Masonry will be very useful if you want to build pinterest like website. It is a responsive dynamic grid support jquery plugin. This will automatically adjust the blocks according to available space on screen.