From the homepage:
Unsemantic is a fluid grid system that is the successor to the 960 Grid System. It works in a similar way, but instead of being a set number of columns, it's entirely based on percentages.
Unsemantic is a fluid grid system based on percentages, SE-Oh? compliant, built with Sass and Compass (drink!), and also supports both
@media queries and Adapt.js to respond and configure your breakpoints.