|Designer(s)||Chris Hazard and Mike Resnick|
|Input methods||Keyboard, mouse|
Achron is the first "meta-time strategy game" (Real-time strategy with time travel) in development, notable for being the first game with free-form multiplayer time travel and its subtle handling of temporal paradoxes such as the grandfather paradox.
When asked about the deemed overwhelming complexity of the game, designer Chris Hazard replied:
While there’s been talk about how complex the game appears, all of our play testers have been able to start using the time travel mechanism within a few minutes of game play. We have designed the single-player game to gradually introduce the player to time travel...
The unique aspect of gameplay in Achron is the fact that the game proceeds not only in many instances of space, but also in many instances of time. Players can simultaneously and independently play in the past, present, or future.
For instance, if the player is attacked at an unexpected spot, they can travel to the past and move their army towards the spot where they now know the attack will occur. Or if the player waged a battle which ended in defeat, they can jump to the past and prevent the battle from ever happening. That said, the opponent may alter the course of events as well in order to counter any changes in history the player made. Chris Hazard states that "the gameplay tends to be a race to the past." Entire battles may take place in the speculative future as well, and players may take a peek at the future to know how matters will be.
Additionally, apart from the player being able to view and command his civilization in the past and the future, individual units may travel through time as well. This process in denominated "chronoporting". When it takes place, the player must be cautious to avoid "chronofragging" his units - that is, having units collide with previous or future instances of themselves (or other units) after travelling through time because they occupy the same physical space at the same time. Thus the player must move their units to deliberately free spaces in the time zone they want to send them to in order to avoid this; otherwise, the weaker of the two units ends up destroyed, with the stronger surviving but receiving certain damage.
Chronoporting is useful as instances of a certain period of time may battle alongside their instances in another time zone, resulting in a way of easily building large armies of time clones. Then again, if travelling to the past, the instances that did not yet travel through time must eventually do so or they will cease to exist.
The main, most notable resource of the game is chronoenergy. It exists as a limitation to players' interference with time. Issuing commands in the past and chronoporting units costs chronoenergy, in order to prevent players from continually and endlessly countering the other's changes in the past and indiscriminately undoing all their mistakes. The deeper in the past modifications are, the more chronoenergy they cost. Chronoenergy is regenerated as long as no commands are made and regenerates faster the closer you are to the present.
Chronoporting may lead to the grandfather paradox. In order to solve this, the game's engine automatically switches between the two possible outcomes. For instance, if a tank travels to the past and destroys the factory that created it, the tank survives and the factory is destroyed with the passing of a time-wave, vice-versa with the passing of another, and so on until one outcome falls out of the boundaries of the timeline and the other becomes the absolute outcome.
Just as there is a mini-map for the player to guide themselves through space, the game's peculiar gameplay requires that there also be a timeline for orientation through time. Attacks occurring in the past or in the future are displayed in the timeline, as well as what point of time opponents are currently viewing and managing.
Changes in history -that is, the past- do not instantly affect the present. Instead, alterations are propagated via "timewaves", in order to give players a chance to react to opponents' changes in the past before they become irrevocable and directly linked to the present.
Three different races (civilizations) in Achron have been confirmed (two are alien and one is human): the Vecgir, which master teleportation, the Grekim, which master time travel, and the humans, which master offense.