Tremulous is a free and open source asymmetric team-based first-person shooter with real-time strategy elements.

Humans utilize various weapons, armor and other upgrades, while aliens may evolve into more powerful classes, each of which possesses unique abilities.

The point at which a stage change occurs varies dynamically depending on the number of players on each team.

In addition to requiring a certain stage, each human item or alien class must be purchased using currency earned in game.

As a mechanism to encourage builders, who naturally don't engage in combat, players are also rewarded currency every two minutes by simply staying alive.

To reduce the likelihood of the match ending in a tie, most games enter a sudden death mode ten to fifteen minutes before the draw/tie time limit.

As they earn frags, alien players can evolve into a new form in order to upgrade their health and gain new abilities.

Tremulous's development by the Dark Legion group commenced in early 2000 as a modification for the commercial computer game Quake III Arena.

The gameplay is generally inspired by the Quake II modification Gloom,[7] which also features alien vs human teams with distinct user classes.

White of the ETPub mod for Wolfenstein: Enemy Territory, contributed an administrative system and a backported client[14] that were soon incorporated into the official Subversion repository.

[17] A Tremulous continuation from Dark Legion has its source code repository migrated to GitHub and is not under active development (last commit June 2016).

[26] Joe Barr of NewsForge called Tremulous his favorite free software FPS game.