A science fiction board game by MB and Games Workshop.
(Note: Translations may be fuzzy, because I've only played the Finnish language versions!)
Space Crusade is basically a "light" version of GW's Space Hulk. It is based on same game universe and has same monsters, too. It is also gameplay-wise and content-wise similar to another MB/GW game, Hero Quest. The creatures of the game are similar - the orcs of HQ resemble space orks of SC, goblins resemble gretchins, the skeletons resemble the androids, and chaos warriors are, well, chaos warriors with modern weapons =)
The basic idea of the game is to mop up some of the unfortunate spaceships that have got stuck in the warp space (the Space Hulks, see) and are now full of unwanted visitors - such as the orks and gretchins (green-skinned humanoid creatures), androids, and six-legged, head-ripping, stylishly-ripped-off-from-Giger Genestealers (that also appear in Space Hulk PC games in Very Large Numbers). And, of course, the Chaos Warriors. Also, the chaos controls the Dreadnought (in my version somewhat less fearsomely "Destructor") that's a Mecha-style robot with heavy weapons - damn hard to kill, too. The "game master" of the game is just a normal player, called chaos player, who controls the enemies.
The other players - up to three, known as Blood Angels (red), Ultramarines (blue) and Imperial Fists (yellow - though in my version they were, for some reason, called "Space Judges") - control the Space Marines (or Universe Warriors or whatever they're called in localized editions). Each player has 4 normal troopers and one mega-tough trooper, the commander of the team.
The troopers all carry normal bolters (can approximately kill an enemy per turn...), except for the "heavy weapons specialist" who carries any of three special room-clearing apparatuses (large saturation attacks and related distributors of lethality). The warriors can also engage in hand-to-hand combat. The commander carries other kinds of weapons (power gloves, axes, heavy bolters, stuff like that) that behave differently... Also, the commander gets specified amount of equipment cards and command cards - equipment cards can be of once-use variety, or stay in play all the time; command cards can be used only once. Different factions have different kinds of cards.
The game is played on a four-part board; the parts are combined to one board in n ways, depending on the scenario. There are doors, corridors, rooms and special sort of rooms on the board - interior of any modern spaceship!
As the marines enter one of the boards, they scan the radars - and the chaos player is busy placing cardboard "radar blip" counters on the board. (the radar blips move on the turn, and as soon any of the marines has a line-of-sight to it, they get exposed and get replaced by whatever monster's picture is depicted on the other side of the counter.) On each turn, the players in turn move (each type of piece moves up to its maximum amount of squares) and fire and/or hit (firing is resolved with special dice; heavier weapons have bigger likelihood of hitting and damaging, of course).
Also, the chaos player draws a card every turn that will often mean trouble for either the players or the chaos player (often also in form of collateral damage to the players).
This game is pretty nice - even though I only played it couple of times, I now have a sudden urge to dig it from the "archives". I must say that these games did influence me somehow: I later got Warhammer and WarZone, and through miniature gaming, I found The Most Ultimate Strategy Game Ever Made, Battletech. So, you see, Space Crusade was a gateway game to harder strategy games. =)
I know that PC/MS-DOS adaptation was created (by Gremlin), but it didn't work too well in my computer - or maybe I found the UI clumsy for some other reason, can't remember right now...
Thanks to Tiefling for assistance.