Alternatives to Chess Second
The FIDE side of chess: any rated player's rating history since 2001, before the round starts. If that's not for you - or you want to try something different - here are apps that overlap on features and use cases.

Chess King Learn
Chess King (CHESSQUEEN INC, ex-Convekta)
Huge Convekta course catalog in one app.
Free
4.8Web · iOS · Android

Chess.com
Chess.com, LLC
The default home of online chess.
Free · from $4.17/mo
4.5Web · iOS · Android

ChessAtlas
ChessAtlas
Build an opening repertoire that survives spaced repetition.
Free · from $6.99/mo
Web

CT-ART 6.0
Convekta Ltd. (ChessOK)
The classic tactics trainer, now multi-platform.
From €24.99 one-time
Web · iOS · Android

Chess Tempo
Chess Tempo
The serious puzzle grinder's tool.
Free · from $3.50/mo
4.7Web · iOS · Android

ChessEndings
ChessEndings
Play endgames out against an opponent that never gives up.
Free · from €39 one-time
Web

Forward Chess
Forward Chess, LLC
Interactive chess ebook reader with embedded engine.
Free
4.8Web · iOS · Android

Lichess
Lichess (charity)
Free, open-source chess. Forever.
Free
4.8Web · iOS · Android