Resequence Engine™ provides the time travel gameplay on which Achron was built.

The Hazardous Software® Resequence Engine™ is a flexible game engine that enables multiple players and agents within the game to perform free-form time travel within a time window. It is a stable, high-performance game engine that can be used to create a variety of different game types beyond RTS. The core gameplay mechanisms, in-game scripting, and user interface are all fully customizable.

Resequence Engine™ Supports Serious Gaming, Training, & Multi-Temporal Decision Support Platform

The technology behind the Hazardous Software® Resequence Engine™ opens up avenues for practical applications beyond time travel in video games. We have received significant interest in using this technology for serious games such as military and corporate applications. The main applications are as follows:


Resequence can be used to teach causality and long-term effects. Because users can play at any point on the timeline, they must constantly evaluate and reevaluate the consequences of each of their decisions. If a user has made a mistake, the user can go back in time, retract commands, and re-issue new commands to the units. Players are thus able to change history, blurring the boundary between hypothetical and committed decisions. In particular, the player can revisit critical decision points, learn what decisions had the most long-term impact, and use statistical information on the timeline to make more informed decisions.

Finding Best-Response Strategies

Resequence’s support for multiple users to simultaneously change history can further enhance training. Each user can take advantage of an opponent’s strategic weaknesses in the past, and each user can correct mistakes in strategy and determine the best response to their opponent. This helps users to find minmax strategies, that is, strategies that minimize the maximum possible loss. Loss of information asymmetry can be severely detrimental to a given strategy, but Resequence pushes users to account for the possibility that their opponent may learn of their strategy before it is executed. Users can look into the future to see what the outcomes of their current strategies and their opponent’s strategies will be.

Qualitative Sensitivity Analysis of Simulations

Given a particular simulation, a user can revisit decision points on the timeline and determine their long-term effects. Seemingly major decisions may turn out to have little impact on long-term effects. Similarly, seemingly minor effects, such as improper etiquette with a local leader, may drastically alter the course of events. Resequence provides a new interface to drive simulations for exploring the effects of decisions.

Collaborative Planning

Multiple users can simultaneously edit a strategic plan, with information on the timeline guiding the users to prevent conflicting plans. Resequence can be viewed in this regard as an automatically merging configuration management system for strategies. The merging of plans is done by time waves, which carry the causality of changes in the past to the future. As events change on the timeline, the statistics depict change and pulse so a user can see how other players are affecting the time line.

Time Waves as a Computation Model

In the abstract sense, threads refer to different computational tasks running at the same time on different parts of some larger task. Time Waves, which are one of the cornerstones of Resequence, turn threads on their side; time waves operate on the same task but at different points in time. Threads and time waves are thus orthogonal and may be combined.

Time waves are a new model to run simulations or even deployed software wherever a user wants to change the history of an application while it is running (e.g., removing a fault that occurred in the past, fast-forwarding the change to the present) or wants to run a simulation which uses its own future output as input for predicting the future (e.g., financial modeling). Time waves may be used instead of or as a complement to reversible computing.

For questions or further info, please contact us at

Questions about Resequence™?