ChessBase 11 - Chess Database Software, Store, Analyze Games, Books, etc

SCID Flathub

▷ How to Use A Chess Database To Improve?

Chess Opening Explorer

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

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

Web Apps

Fritz Powerbook Chess Game Database 2018 - Chess Database Software bundled with Chess Masterpieces CD

How To Use The Opening Explorer - by Nate Solon

How to Use Chess Engine and Databases Like a Pro - TheChessWorld

Opening repertoire study with spaced repetition (+ database and game collections) - Chess Forums