Osmos is being put out by Hemisphere Games, and there are far worse things you could do with an hour than trying out its free demo.
You play as a little glob of matter, possibly some kind of microbial lifeform. You can crash into blobs that are smaller than you to absorb them, and grow in size, but contacting a blob which is bigger than you will result in you getting eaten.
You move by firing off some of your mass in the opposite direction; losing mass in this way makes you smaller, but can put you on a trajectory to absorb other blobs. When you're smaller, you're faster and more manoueverable, but when you're larger you're in less danger of getting eaten.
The demo's quite short - you can blow through it in about 30 minutes - but it sells the concept well enough. The controls are simple, the ambient music is relaxing, and the gameplay is compelling. Like all the games I've been talking about over the last few days, it's a 2009 Independent Games Festival finalist, and it appears to be one of the better ones, so go get your hands on it and form an opinion for yourself.