Chess Opening Basics: The Scotch Game - Chessable Blog

Catastrophes & Tactics in the Chess Opening - Volume 3: Flank Openings: Winning in 15 Moves or Less: Chess Tactics, Brilliancies & Blunders in the Chess Opening (Winning Quickly at Chess): Hansen

The Classical Sicilian Defense - Chess Opening Trainer on DVD

Chess Openings Trainer - Quick Start Guide

Chess Position Trainer - Lubbe Schach

Lichess just added opening training (in addition to their tactics trainer). Check it out! : r/chess

Opening training with Fritz 17

Chess Trainer Hub - RagChess

CHESS BOOK: CHESS OPENING TRAP OF THE DAY by Bruce Alberston 9781580422178

Fritz Trainer Software

EP 290- Dutch Trainer and Author IM Jeroen Bosch on How to Build an Opening Repertoire — The Perpetual Chess Podcast