Startup Design Framework:
http://designmodo.com/startup/?u=111

Bootstrap:
http://getbootstrap.com/

Foundation:
http://foundation.zurb.com/

YAML 4:
http://www.yaml.de/

Gumby:
http://www.gumbyframework.com/

Kube:
https://imperavi.com/kube/

GroundworkCSS:
https://groundworkcss.github.io/

BASE:
http://getbase.org/

Wirefy:
http://getwirefy.com/

TukTuk:
http://tuktuk.tapquo.com/

Skeleton:
http://getskeleton.com/

Responsive Aeon:
http://newaeonweb.com.br/responsiveaeon/