Chess Database - Opening Master

Best Chess Openings for White & Black (42 Openings)

Chess Games Database Online

Réti Opening - Chess Openings

Chess Opening Database - Shredder Chess

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

We made a tool that lets you search the lichess game database by chess concepts. Link in the comments : r/chess

Does the win/draw/loss rate from the opening database also apply to lower rated games? - Chess Forums

Batsford chess openings 2 (The Macmillan chess library)

Small Encyclopedia of Chess Openings ABCDE on CD (3rd Edition) Chess Software

Chessbase - Opening Repertoire Management Part 1