This is called the "diamond" crystal structure that atoms from column IV of the periodic table assume. Crystalline carbon (a.k.a diamond) has this structure, but so do the semiconductors silicon and germanium.
Click the buttons at the top of the model to show either a full cube of crystal, or a smaller piece with labeled facets, or the atoms of a single "unit cell" (the basic building block of the crystal).
The lower buttons turn off and on XYZ axes and the boundaries of the unit cell.
Drag the mouse across the model (repeatedly) to rotate it.
Restore its position with the reset button.