Chess against an engine written by hand: legal move generation with castling, en passant and promotion, check and mate detection, an alpha-beta engine with iterative deepening and a small evaluation, four difficulty levels, PGN import/export, an opening-book of a few hundred lines, and a puzzles mode from a seeded set. The board is keyboard and touch playable; games are saved and resumable by URL.
Chess against an engine written by hand: legal move generation with castling, en passant and promotion, check and mate detection, an alpha-beta engine with iterative deepening and a small evaluation, four difficulty levels, PGN import/export, an opening-book of a few hundred lines, and a puzzles mode from a seeded set. The board is keyboard and touch playable; games are saved and resumable by URL.