Customizable & Responsive Grid System: 34Grid
34Grid is a grid system for responsive layouts which is based on "equally distributed columns" for each row.
There is no built-in CSS reset (so that you can use your own) and there are rules for handling images + video.
Also, there is a "how-to" in the resource's website for handling social widgets which can be very handy.
34Grid is completely customizable. We can define the number of max columns, margin between them, margin between rows and transitions between columns.
Once the custom options are selected, a unique build is created instantly and ready to use.