The Tool Palette is your central command center for launching tools, closing them, changing colors and modes and even flipping the palette.
You can also use the
Spacekey to flip between vertical and horizontal layouts.
The palette has enough indicators to tell you which tools are open and which one is currently active.
There is also a special mode where you can hold the
Optionkey and click on a tool to launch multiple instances. This only applies to the Lens and Ruler tools which support more than one instance. The instance count can be seen as a badge on the tool-icon.