Warhammer 40,000 is a miniature-based table-top battle game in 35ml scale made by Games Workshop, which is currently in its third edition. It is a futuristic version of their Warhammer fantasy game, which takes a setting similar to Middle Earth and adds in a number of new races, notably the evil forces of the Chaos gods. In the 40k universe, most of the usual fantasy races are present, but in a somewhat altered form, as well as a couple of extra races.
Humans are represented by the bio-engineered superhuman Space Marines, the rank and file of the Imperial Guard, who show all the tactical savvy of the armies of World War 1, and the giant robotic fighting machines of the Titan legions. Sadly, the Titans don't appear in the small-scale firefights represented in 40k. The humans are led by the immortal Emperor of Mankind, an immeasurably powerful Psychic who brought order to the humans of the galaxy in a mighty crusade ten thousand years ago. He was mortally injured when his most trusted general turned to the evil gods of chaos, taking half of the space marines with him.
Elves and Dark Elves are present also, in the form of the technologically advanced but nearly extinct Eldar, who wander the stars in great spaceships called Craftworlds, and their evil Dark Eldar counterparts. The Dwarves of 40k are called Squats, and are hardy miners whose human ancestors settled on worlds with high gravity and adapted to be short, stubborn and tough. The Orcs are also present, except it's spelt Ork, and they're boisterous and carefree green-skinned creatures who love nothing more than a good fight. The Tyranids are evil space beasties which evolve by assimilating the DNA of other lifeforms and using it to create bizarre new hybrid creaures, all of which look suspiciously like the Alien from the film of the same name. The frankly rubbish Necrons are a failed attempt to make a whole race based around a t-800 terminator, and finally, the Tau are a new race, and appear to be unique for a games workshop race in that they are not obviously derivative of other well-known sci-fi or fantasy. Oh, except that they have large combat suits that look exactly like small battlemechs. And a V-Tol tank that looks just like the dropship from Aliens. So not at all derivative, then.