Semantic UI - A UI Component library implemented using a set of specifications designed around natural language
UIKit - A lightweight and modular front-end framework for developing fast and powerful web interfaces
w2ui - W2UI is a small JavaScript UI library with a complete set of widgets: layout, grid, sidebar, toolbar, tabs, fields, popup, utilities.
Kendo UI - Fast, light, complete: 70+ jQuery-based UI widgets in one powerful toolset
JQWidgets - Unique toolkit for HTML5 Web development
jQuery UI - Curated set of user interface interactions, effects, widgets, and themes built on top of the jQuery JavaScript Library