The Diablo 2 Wiki
The Diablo 2 Wiki archive is available for anyone looking for information on Diablo 2. All information here is pre-D2R but contains a lot of useful information that is still relevant. Updated sections for new D2R features can be found on the PureDiablo Diablo 2 section

Cube Open

From Diablo 2 Wiki

A shot of the Horadric Cube in action in Act Three. A right click on the cube opens up the window that takes up the left side of your screen.