Chess4D

"4D chess" is usually a joke about overthinking. Chess4D takes it literally and makes it playable. The board is 4×4×2×2: four small 4×4 slices joined by two extra axes, 64 squares in all, the same count as a normal board. Pieces keep their familiar logic: a rook changes one coordinate, a bishop two by the same amount, a knight jumps two along one axis and one along another. The interface shows the position as a hypercube projection or as four flat slices. Start with the 20-piece exploration army and leave the hints on, because a bishop that seems blocked often has a path through another slice. The practice computer answered our first pawn move with a move across both extra axes, which is the lesson of the variant in one move.

The 3D page is the least interesting of the three for a chess player. It is ordinary chess beside a rotatable 3D board, and it does run genuine Stockfish 18 in the browser with an analysis panel. But the engine has no strength levels, the game disappears on refresh, and Lichess already offers a 3D piece style and eight engine levels. Use it to show someone the 3D board, not to train.

The 5D mode is the reason to bookmark the site. It is an unofficial browser take on 5D Chess With Multiverse Time Travel, the paid Steam game by Thunkspace: moves can go back to an earlier board and open a new timeline, and a turn is only complete once the present has moved to the opponent and every king, including copies in the past, is safe. The rules page credits an open-source engine as its reference, and five guided exercises teach the ideas one at a time. Chess in 5D (chessin5d.net), an older open-source implementation, covers similar ground. Chess4D's version is two players on one device only, carries an "experimental" label, and says itself that compatibility with the commercial game is still under review.

The weak point is who runs it. The site names no person, company, country or contact address, the domain dates from September 2026, and the footer is lined with launch-directory badges. Google Analytics loads on the first visit with no consent prompt, and the privacy policy says nothing about it. Nothing is sold and play needs no account, so this costs a player little, but an account is only worth creating to save 4D games. This review is based on playing all three modes as a guest; we did not create an account.

For a club player who wants to see what the chess-variants corner of the internet has to offer, a 4D game against the practice computer and the five 5D lessons are a good free hour. For improving at standard chess, look elsewhere.