These are UI elements built on top of (a shim for) the coming standard Web Components. For another Web Components shim check out polymer-project.org along with

These are UI elements built on top of (a shim for) the coming standard Web Components. For another Web Components shim check out polymer-project.org along with a small, opinionated framework leveraging Web Components. Especially look at the awesome Sandbox application allowing you to compose web components :)