Mecca is a new browser by the prolific Todd Ditchendorf of Fluid fame. It is currently in the works, and features:

• Open Plug-in Architecture
• Built-in Userscripting
• Userstyles
• ÜberView for Plug-in Split Views
• Global Keyboard Shortcut
• Single-Window Browsing Mode
• BrowsaBrowsa Plug-in for Sidebars
• Session Restore
• Full-Screen Mode
• Customizable Shortcuts
• Integrated Gears-loading (InputManager)
• Hidden “Closed” Windows
• Thumbnail Plug-in for CoverFlow
• TinyURL creation/expansion
• Automatic Software Updates
• Custom User-Agent Strings
• Full WebInspector
• Custom Window Opacity/Level/Style

It looks very interesting!