Tremulous is a first person shooter featuring two opposing teams, human and alien. Both teams are able to build structures such as spawn points, which are vital to their victory. The goal of Tremulous is to eliminate the opposing team and all of their spawn points.
Each team in Tremulous differs fundamentally from the other. The alien team is class-based, with two classes initially available: the alien team’s builder, known as the Granger, and the Dretch, the weakest offensive alien. The aliens are awarded frags for killing their foes which may be used to evolve into stronger classes, capable of greater and more varied maneuvers. In contrast the humans are upgrade-based, receiving credits for kills that may be exchanged at an Armoury structure for new weapons, armour and equipment. Two such upgrades are available for free: a rifle and a construction kit, used for building structures.
During a game of Tremulous, each team occupies one of three stages of development. These stages are reached by accruing more than a specific total number of kills by the whole team. Each new stage unlocks new classes, upgrades and buildable structures. If one team reaches a stage significantly earlier than the other team it stands a better chance of defeating the opposing team.