Way to steal my karma.... :)<p>As the original author of this, I was going to put it into a much more presentable state before showing it off here.<p>For those confused, here's a proper explanation. No real-world thing can actually be Turing complete (able to express basically any computation that we might want to perform of any size). That's because there are finitely many atoms in the universe, so we can only construct machines of finite size.<p>It's well known that Rule 110 (Google it) is Turing Compete.<p>What I've done is made an implementation of Rule 110 in HTML and CSS. Since CSS can't actually really manipulate state, some user interaction is required to "drive" it. In the one that bgruber linked to, it's clicking.<p>Here's a bigger version that doesn't require the user to know where to put his mouse. The tab-space combo is just as legitimate as requiring that you plug a computer into a wall to power it in order to run a Java program. <a href="http://elilies.com/rule110-full.html" rel="nofollow">http://elilies.com/rule110-full.html</a><p>Also, I haven't tested it on anything besides the latest Chrome on Mac.