UIBox - it seems to me a very good initiative. Almost any Web UI component that we can think of has already been built by someone.
A search on Google results in hundreds of results. All this is great!
Except for a few problems: no demos, poor documentation, dependencies conflicts, browser support, etc.
The UIBox initiative tries to help solving this problems. To start with, UIBox is a curated HTML, CSS, JS UI component library. There are a few requirements to a given component be present in UIBox:
You can check the motivations and reasons for the UIBox initiative.