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

Single player

From Diablo 2 Wiki

Single player Diablo 2 is when players play offline. A whole community has spawned from Single Player where they play by their own rules and guidelines.

The Single Player community can be found in the PureDiablo Single Player forum.