I'm working on a Ribbon component that utilizes Prototype. The Ribbon I'm referring here is the Ribbon UI in Office 2007. Toolbars are passé.
Here is a highlight on the key features of the Ribbon component:

• Multiple tabs, multiple groups
• Collapsible
• Stickybar that is persistent to the left (like the "Quick Access Toolbar" in Office), and a specific Help button
• Detects mouse wheel scrolling and switches tabs
• Supports different modes where different tabs are available