Imagine the free-form digging and construction of Minecraft on an alien planet, where you can build up into space, with physics-simulated movement, vehicles, guns, alien wildlife, and laser turrets, and you're coming close to the ideas indie developer CodeHatch is playing with in StarForge. If you're excited, and you should be, you can have a bash in a playable "very early alpha" version. It's rough, certainly, but well worth your attention.
As well as the ubiquitous survival mode, where you must, well, survive on the hostile planet, CodeHatch is planning 'Fort Wars.' The team-based mode will have players gathering resources, building forts, and laying defenses, with the goal of smashing the other team's all-important vats. Sure, you could simply build big guns and smash into them, but you could also tunnel in.
Download the survival mode alpha build here from Shacknews. It may run slowly, and is glitchy and unpolished. The current build also presents you with a white screen for a worrying length of time while it generates the world, but there's enough to be excited about the possibilities.
StarForge will be free-to-play, selling new skins, classes and items which CodeHatch insists will merely offer players more options, rather than make them outright more powerful.