Software
w2ui
W2UI is a small JavaScript UI library with a complete set of widgets: layout, grid, sidebar, toolbar, tabs, fields, popup, utilities.
Marko Widgets
Marko Widgets extends the Marko templating engine to provide a simple and efficient mechanism for binding behavior to UI components rendered on either the server or in the browser.
jKit
A very easy to use, cross platform, jQuery based UI toolkit, that's still small in size, has the features you need, and doesn't get in your way of doing things!