The Liquid Laser correctly guessed my game for today: Descent.
In this game you play a pilot of a spacecraft that is trying to destroy some mining asteroids, on which the mining robots are gone crazy and attacking humans. To avoid a bigger threat you blow up the asteroids. To do this you have to shoot robots, rescue personel and navigate mining tunnels in true 3D. Your ship operates at zero gravity and you have full control over all movements, so you have six degrees of freedom. This means you cannot only go forward, backward and left and right, but also up and down. You can turn not only left and right and up and down, but also turn around yourself. This can be very disorienting. It is hard to recognize a room you was before in, if you come to it from another tunnel and are now turned upside down. Luckily you have an automap to help you:
Oh shoot. Your mission in each level is overloading the reactor core (by shooting at it) and then it goes into self-destruct sequence navigate to the exit. It is helpful if you found the exit before and memorized the way from the reactor to the exit, because if you get lost and don't leave before the countdown is up, you die with all the mining robots.
This game was immense fun, the challenge of navigating and orienting in these mining tunnels while on the threat of being attacked by robots kept you on edge. Music was good. This game had fully 3D enemies, in difference to Doom and fully 3D-environments - Doom in difference had always horizontal or vertical surfaces, never something slanted. So Descent was a big step-up in level-design.
I read on Wikipedia that the source code was released later, leading to ports to more modern platforms including Oculus Rift and Wii homebrew channel.
This video must have been shot with a later modified source, as the resolution is upped, the other content is still original though:
Last edited by Mnementh - on 16 November 2017