http://www.darwinia.co.uk/

This looks like a very interesting games. It's avaliable for "purchase" on a few "online stores" for a pretty cheap price. I believe though that a game like this would totally be worth buying legtimately as its independently programmed and it's pretty original.

A friend of mine at work was addicted to this for a few months after he bought it, although I never really got to grips with it (too lazy). Don't think he plays it much now but you know how it is, you buy something new, use it constantly for a week or two then forget about it for months before digging it out again and starting all over again

In principle though, very original and very good, or so I hear