The Design Center included with AutoCAD several versions back can be used for many purposes. To launch it you can use the ADCENTER command or the alias DC.
First consider it as a Symbol Manager. You can navigate to a folder in the left pane and it fills the upper right pane with the symbol drawings in that folder, with a small preview. Clicking on one of the icons shows a larger preview, then dragging the icon to the AutoCAD drawing window initiates the insert process.
Next is symbol table imports, such as layers. Navigate to a folder on the left pane, click the [+] box to the left of a drawing and the tree will expand to the available tables. For example, clicking the Layers item under the drawing shows all the layers for that source drawing. Select one or more layers and drag them to the drawing window and they will be created in the current drawing. Objects contained in the source drawing will not be imported, only the definition (including the default color, linetype, etc).