I stumbled upon the Skeleton CSS framework when I was trying to find a responsive css framework. I thought it was a pretty clean system and may use it in a future project. So I got a jump on things and converted their CSS files into SASS so it was easy to use.
Great project from the people over at Twitter. The Bootstrap is a fairly complete system with some very clean designs, web elements, and handy javascript components. I thought I would go ahead and convert the LESS code to SASS for use in my projects.