* Flexible particle system - 99% of the in-game visual effects are configured using particle scripts.
* 16 buildable structures with in-game functions.
* Play as several alien classes with unique abilities.
* Customize your setup as a human and buy new weapons, armour and items.
* Scale the walls and ceilings as an alien waiting for an unsuspecting human.
* Realistic physics and motion - no bunny hopping or quick back peddling.
* Flexible map system - animated mapobjects, triggering, light flares, etc.
* Large weapons system - don't like the weapon you have? Sell it and buy a different one, dozens of options.
Tremulous is a first-person shooter with elements of real time strategy, featuring two teams - humans and aliens. Players must build and protect a base which is essential for their survival, consisting of working buildable structures which provide various functions, the most important of which being the ability to respawn. Victory is achieved by destroying all enemy spawn points and eliminating all members of the enemy team.
During a match, most players engage in fighting the enemy, while others are responsible for base maintenance and construction of new structures. In order to defeat the enemy, humans utilize various weapons, armor and other upgrades, while aliens may evolve into more powerful classes, each possessing unique abilities.
The teams do not have access to all possible upgrades and buildings at the beginning of the game. Each team must accrue a number of kills in order to advance to the next developmental stage. The point at which a stage change occurs varies dynamically depending on the number of players on each team. Each new stage brings more upgrades for the humans and more classes for the aliens.
In addition to requiring a certain stage, each human item or alien class must be purchased using currency earned in game. Alien currency are officially called frags, although players frequently refer to them as evolution points or evos. The Humans gain credits. Players earn currency by killing enemy players or by destroying key enemy structures. Amount of received currency depends on how upgraded the opponent was (or which structure was destroyed) and how much of the target's total damage was dealt by the killing player. As a mechanism to encourage builders, who naturally don't engage in combat, players are also rewarded by currency by simply staying alive for certain amount of time.
Builders are responsible for construction of new buildings and base maintenance. Each building takes up a certain number of build points available to each team. The number of build points can vary from map to map and server to server, limiting how large bases can become. 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. This is a period during which the building of most or all structures is prohibited, allowing attackers to more easily overwhelm the defenders. - Wikipedia.org