Tabbed panels in action. All of these panels can accept new tabs, but the only panel currently with multiple tabs is the Object Properties in the Top Right - It has Material and Lighting in the other tabs. These will all get little icons in the end. This is actually looking more like 3.0 again!
The bottom row of Toolbox buttons switches the Tools panel beneath it. These represent the main activities you work in during a projects workflow, so I'm hoping you won't need to switch often. As the move/rotate tools are used so often they sit in the main Toolbox.
The layout is fairly flexible - you can for instance shrink the toolbox to a single column of icons, and undock the tool options. And scaling the icons and fonts works too.
Also seen here is a new toolbar - I'm looking at this as a beginner's toolbar as I'd recommend learning the keyboad shortcuts for these frequently used things - you can hide it once you've done with it, or swap out the basic tools for other commands/tools you use frequently.
All the panels/menus/toolbars vanish when you press TAB for a clear viewport.
The other small addition here is the text entry box in Groups - where you can search for objects by name, or multiple objects by prefix. Handy for large scenes.
