Before I do that, though, let me briefly discuss their similarities. They are both essentially two dimensional Minecraft, where it looks much more like a platformer than it does an open world. They are both online, of course, but Starbound is a bit different. There aren't single, randomly generated worlds in Starbound. Instead, there are over four hundred quadrillion planets that have been randomly generated, but everybody is kind of thrown into the same 'universe', technically speaking. To my knowledge this means that the star on coordinates X32, Y71 will always yield the same planets whether you're playing single player or online. In that sense, though, the dismay one may have for always playing in the same universe as everybody else is dispelled due to the fact that you are virtually guaranteed to explore planets nobody else in the game has ever even seen before.