AdRoll UI Framework – Style guide by Mason Lee
Flat Colors UI Framework PSD by Designers Revolution, via Behance
AdRoll UI Framework – SiteUp
Flat UI Pro is made on the basis of Twitter Bootstrap in a stunning flat-style, and the kit also includes a PSD version for designers. From $39. Learn More: http://designmodo.com/flat/
Project style guide template – SiteUp
Material Kit is a Free Bootstrap UI Kit with a fresh, new design inspired by Google's material design.
The most powerful webapp UI framework for developers and digital product makers
Multiple selection dropdown | Semantic UI