Dyson is a 4X (explore, exploit, expand, exterminate) space game with unusual technology and a curiously serene feel. You play an alien lifeform that colonizes asteroids, but competitors are doing the same (RTS-like), and your ultimate goal is to exteriminate them.
Your mobile units are "seedlings," which both battle enemies and can be used to build "trees" on asteroids; it takes 16 seedlings to initiate a tree. Trees are of two types -- ones that create more seedlings, and ones that grow defensive pods that are launched at enemies attacking your asteroid. Asteroids range in size and energy, and can each support between one and five trees.