ChessDB - a free Chess Database

Chess Openings Database

Shane's Chess Information Database - Wikipedia

Lichess Database: Which openings are most successful : r/chess

sql - Databases for chess games - Stack Overflow

Best 5 free Chess Software - Chess Forums

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

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Opening Tree Which chess app?

Quantifying the complexity and similarity of chess openings using online chess community data