Game type: web based
Time demand: Very small
What it is:
This isn't really a straight-out game like most of the other links, and is in the rocky stages still of its re-birth, but I enjoyed it enough in its previous incarnation and it's neat enough that I'm linking it, anyhow. So there.
The best description of this would be, I suppose, a hands-off creature simulator. You create a carnivore or herbivore out of various creature parts, and then send it out into the little technosphere world to fend for itself. Your creature must eat, fend off (or outrun) any attackers, and may eventually mate and bear children before finally dying of old age (or sharp pointy teeth, or defensive horns, or whatever).
That's... basically it, honestly, but it's pretty neat. I think. Like I said, it's been not running too well in its re-incarnation (it was around many years ago, then was offline for years, and just came back around again semi-recently). But it's an entertaining way to spend a little bit of time, and something to check up on now and then on the net.