The "2&3D" tools are tools that are relevant to all the modules. They are not limited to 2D or 3D modules, hence the "2&3D".
They include:
The memory manager informs you of how much memory is available for the application and how much memory is used by different parts of the application. It is also responsible for automatically deleting low priority memory buffers when the application needs more space.
This tool enables you to select/de-select frames. It is the only way to do so in 3D windows.
This tool enables you to open multiple windows. Each window can be used to display different frames in different modes.