ChessAssistance.com Chess Openings 2003 Review

The Best Openings for Rapid Chess Improvement - Gautam Narula

learning - Where can I find free training tools like detailed annotated chess openings, middle games and endgames in the PGN format? - Chess Stack Exchange

Opening Database for iphones - Chess Forums

Fritz 15 Help

All 1d6 Opening Repertoire Collection (6 Digital DVDs)

ChessBase opening tree statistics

what do the numbers for each variation in chess opening mean by? - Chess Forums

Building Chess Opening Repertoire - Step 1 - Getting reference database

Opening Move Popularity by Elo, using new Lichess Database data that goes down to 600 Elo : r/chess

Chess Repertoire Explorer