Gameplay in Fort City centers around various free-roam open worlds, visiting locations and interacting with the local inhabitants. Travel between the worlds is possible using the TPM, or Time Portal Manipulator. Occasionally, inhabitants will be immersed in dilemmas which the player may choose to solve in order to acquire experience points. Fort City deviates from most role-playing video games in that it often allows for the player to complete tasks in multiple ways, often choosing solutions that are unconventional or even contrary to the original task, in which case the player may still be rewarded. Players will encounter hostile opponents (if such encounters are not avoided using stealth or diplomacy), in which case they and the player will engage in combat.
The player's effectiveness in combat relies on the use of weapons and armor, which are usually found by defeating other opponents, but can also be found in certain chests. Weapons and are assigned to each hand, allowing for dual-wielding, and can be swapped out through a quick-access menu of favorite items. Shields can be used to fend off enemy attacks and reduce incurred damage, or offensively through bashing attacks. Blunt, bladed and hacking weapons can be used in close combat and each have specific advantages and roles; for example, the player can perform power attacks with each weapon. Ranged weapons may be utilized in long-range combat, but can also be used as a defensive melee weapon in close combat.
The player starts being able to carry only six items at once. Shortly after, they find a small backpack that allows them to carry 25 items. A medium-sized backpack will let you carry 40, and a large backpack will let you carry 60 items.
A diverse selection of recruitable NPCs can be found to aid the player character in the post-apocalyptic wasteland. Helpers include pets and sidekicks. These helpers will follow the player throughout the game and will help take on enemies. Like the player, each helper will have a health bar, and if the bar runs out, they will be transported back to Uncle Cyence's fort, where they will have to wait a while to recuperate. Sidekicks can be given weapons, armor, and more throughout the game, and certain pets can be rode, depending on it's size.
The game takes place in the not-too distant dystopian future set in 2042. A series of horrible natural disasters led to a majority of the world's population being wiped out, and leaving only a few areas hospitable. One of these locations is a huge city known as Fort City. In Fort City, the economy has been completely destroyed, forcing most people into looting and thievery. Because of this, people have a need to build fortresses in order to protect both themselves and their belongings, hence the name, Fort City. The leader, and the reason the economy broke down is a wealthy, charming "mayor" named Jack Fort. Jack Fort possesses a majority of the wealth in Fort City, and lives in the VIP-only wealthy district of Forthaven. He owns his own police force/military called "The Enforcers" which is led by Lt. Gaston. He also owns his own monorail that circles the entire city which people believe he uses to relax and watch the civilians of Fort City suffer.
The protagonist is a young inhabitant of Fort City named Zach. Zach lives with his Uncle, Uncle Cyence, who is one of the more successful people in Fort City, who once owned a science industry which collapsed along with the economy. Uncle Cyence is working on recreating a time machine prototype that he almost finished before the collapse. After finding all of the parts with the help of Zach, he realizes that anyone over certain age was unable to enter a time wormhole, or it would have unknown, horrific consequences. Zach is just young enough to be able to go through the wormhole, so after preparing him for his mission, a fatal accident occurs, sending various inventions throughout time. Zach must go back in time and retrieve these inventions at any cost. Cyence explains that in order from rewriting history, he is creating a duplicate timestream that Zach can to anything without having any effects, and tells him to use that timestream to find the invention, then go to the real timestream and remove it flawlessly.
- Fort City: 2042 AD, a dystopian city ruled by Jack Fort.
- Prehistory: The Dawn of man, but due to the time paradox, has been randomly receiving objects and people from Old Western America.
- Ancient Greece: Roughly 1240 BC, Zeus is rogue and attacking Mt. Olympus, and due to the paradox is being helped by Odin and Osiris.
- Medieval England: 1006 AD, two kingdoms are at war and Zach must side with one.
- Age of Piracy: Takes place in a port city under British Rule. Not too far away is a small archipelago containing strange formations.
- The Future: 2062, where most of human life has been killed in an alien invasion. A group of survivors is led by Zach's future self.