Outsider is a card game that combines cooperative and hidden traitor mechanics with set collection and hand management, in an immersive science fiction setting.

Players are each assigned or choose a character, each with unique abilities and a different combination of the four skill icons. Each player is also given a random Loyalty card, which is kept secret from the other players. Most players will be Crew and will work together to complete repairs, represented by Goal cards. Crew members win the game when they have completed more goals than there are players, all Crew have at least one completed Goal, and any Crew member correctly declares victory on their turn.

One or two players will be Outsiders. Outsiders win the game if they declare victory on their turn and all Crew members are Doomed. All players lose if the deck runs out or if everyone becomes Doomed from a single source, which adds a cooperative element. An addendum provides alternate rules for groups that find this too harsh or would prefer a more narrative ending.

The setting is gritty sci-fi with art by James Zark lending a cyberpunk flavor to the characters. The basic concept deals with a future where vessels move between universes to save time on space travel, with the occasional side-effect of crew members becoming murderous and paranoid, called "Outsiders".

Outsiders are literally castaways from other dimensions. Having shifted between universes too many times, they suddenly find that they no longer recognized things that should be familiar. Torn from a discarded reality, their only option is to seize control of the ship and reverse the shifts in reality, dooming the rest of the crew in the process.

The game lends itself to a wide variety of strategies, and despite a small learning curve the basics come into focus pretty quickly. Multiple playthroughs reveal increasingly complex possibilities, and each game is distinctly different as new combinations of Loyalties and characters are explored.