5D Chess with Multiverse Time Travel

5D Chess with Multiverse Time Travel is a 2020 chess variant video game released for Microsoft Windows, macOS, and Linux by American studio Thunkspace. Its titular mechanic, multiverse time travel, allows pieces to travel through time and timelines in a similar way to how they move through ranks and files. The game was met positively by critics and was praised for its complex and elegant design.
Gameplay.
"5D Chess" begins each game with an ordinary chess setup. As the game progresses pieces can, following specific rules, be moved onto a past version of the board. To prevent time-travel related paradoxes, instead of changing the "original" past, this time travel results in the creation of an alternate timeline or "parallel universe", for which the starting position is the same as the corresponding time-point in the original timeline but with the time-traveling piece added. Pieces can also be sent between these different "timelines" and, when moving across timelines, can move into that timeline's "past", "present", or "future". Whenever a new timeline is formed from a movement of a piece between different times of the board, the player has to make a move for each timeline created, e.g. if there are 3 separate timelines, each turn consists of 3 moves. The game ends when the number of valid moves available for a player is less than the number of timelines, in which case that player loses. In general, the more moves have elapsed, the more complicated the game gets due to the creation of the new timelines.
The rules of piece movement are generalized from standard chess rules, with time and timelines being axes of movement, as with ranks and files. For example, a rook can move any number of squares along one axis, so a player can send the rook into its current position, but any number of turns in the past, using time as an axis of movement. Bishops move any number of squares in exactly two axes, so it is possible, for example, to move a bishop three squares vertically and three turns into the past. Knights move two spaces on one axis and one on another axis - for example, a knight may move to any adjacent space (one) into a timeline that is two timelines away (two). Kings move one in any number of axes. For example, a valid move for a king is to simultaneously go one space over horizontally, into a timeline that is "adjacent" or one move away, and one turn into that timeline's past. Queens move any number of spaces equally on any number of axes. A valid move for a queen could be moving 4 spaces vertically, 4 horizontally, into a timeline that is 4 timelines away, and 4 turns into that timeline's past. Pawns can move through time and timelines under certain conditions. In addition to the standard six chess pieces, the game includes its own fairy chess pieces, the unicorn and dragon (which can move any number of spaces equally through exactly three or four dimensions, respectively) and the princess (which moves like a Queen but is restricted to a maximum of two dimensions of movement). These pieces can be used in alternate board configurations, as in addition to matches on regular 8×8 boards, the game also supports games on 4×4 boards, 5×5 boards, 6×6 boards and 7×7 boards and a puzzle mode. The game can be played online against other players or offline against an AI.
Release.
The game was launched on 22 July 2020 on Steam. It was developed by Conor Petersen and Thunkspace. Petersen said that he had enjoyed chess variants such as three-dimensional chess and conceived using time as an additional dimension for piece movements. He said: "From there, I tried to solve each problem or paradox I found".
Reception.
"Kotaku" reviewer Nathan Grayson called the game "remarkably elegant for what it is". Arne Kaehler, of ChessBase, noted that while the game ran well and is a fun chess variant, the opponent AI was not very competent. A "Digitally Downloaded" reviewer noted that, due to the increasing complexity of the game as turns pass, it presents a "limitless well of possibility". Christopher Livingston of "PC Gamer" called the game "mind-bending". Jacob Aron of "New Scientist" wrote how the game "isn't for the faint-hearted" and "is brain-meltingly hard". Grandmaster Hikaru Nakamura played the game when appearing on VENN in August 2020.