Best chess apps for opening preparation
You're serious about building a repertoire and drilling it until moves are muscle memory. Look for repertoire tools, spaced repetition, and engine depth.
Chessable
Chessable (Chess.com)
MoveTrainer + spaced repetition for openings and tactics.

Chess King Learn
Chess King (Convekta)
Huge Convekta course catalog in one app.
Chess Position Trainer
Stefan Renzewitz
Veteran flash-card repertoire trainer for desktop.
ChessBase
ChessBase GmbH
The professional's database and analysis suite.
ChessMood
ChessMood
GM-led video courses plus live coaching community.
Chessify
Chessify AI
Cloud-powered Stockfish analysis on your phone.
Forward Chess
Forward Chess, LLC
Interactive chess ebook reader with embedded engine.

Listudy
Arne Vogel
Free open-source spaced repetition for openings.

Scid vs. PC
Steven Atkinson and contributors
Open-source database and analysis powerhouse.
Chess Tempo
Chess Tempo
The serious puzzle grinder's tool.