USS Darkstar is a 1999 Canadian Half-Life mod created by Neil Manke and his development team, largely based in Canada. The mod follows Gordon Freeman and several other scientists on board the USS Darkstar in the year 2066, a large exploratory starship that resembles the Nostromo from the movie Alien. Very early in the game, a security guard is injured on an away mission to a nearby planet and is taken into the sickbay.
When the scientists are operating on the guard, a headcrab bursts from his chest cavity (coupled with the Nostromo look of the USS Darkstar, this was most likely also inspired by Alien) forcing the scientists to activate the incinerator. The flame jet kills the headcrab but also detonates a fuel canister, which creates a chain reaction.
This causes a surge which badly damages the USS Darkstar's main computer, deactivating all the force fields and letting loose the aliens. The aliens kill most of the crew, but Freeman manages to reach an escape pod and escape the ship, shortly before it explodes. The game ends with Freeman's pod heading towards the nearby planet, pursued by a large alien vessel.
At least one other scientist also survived the destruction of the USS Darkstar. During Freeman's entering of the labs, the escape pod elevator can be seen through the window, down which the scientist is heading. When reaching the escape pod launch room, one escape pod has already been launched.
USS Darkstar was selected by Valve Software for presentation at the first Half-Life ModExpo at San Francisco in 1999.