http://www.dyson-game.com/
Originally known as Dyson (inspired by
Dyson Trees and
Astrochicken, both theories proposed by theoretical physicist
Freeman Dyson), Eufloria is a simple RTS-ish game where you colonise asteroids in space by planting trees. The tree's leaves then fall off to become your game units. The graphics are totally sweet and the atmosphere has a wonderful vibe.
The games' Steam page is
here. It's released in a day and a half, but if you pre-order it before then you get 25% off.
There's also an old, freeware version
on the game's website that is apparently not representative of the final game, but should give an idea of what it's about.