Tremulous is based on the ioquake3 engine and the source code is available to everyone, so it’s totally free!
Tremulous is a first-person shooter with elements of real time strategy. Each team must construct and defend a base, consisting of structures which aid the players in some way. In order to destroy the enemy, humans utilize various weapons, armor and other upgrades, while aliens may evolve into more powerful classes, each of which possesses unique abilities. Each team must reach a threshold of frags in order to advance to the next stage. Each new stage brings more upgrades for the humans and more classes for the aliens.
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