Universal Paperclips

Frank Lantz's Universal Paperclips is built on the paperclip maximiser thought experiment, and it takes the premise seriously enough to become a real game. You begin by setting a price and making paperclips by hand. What it turns into over the following few hours is genuinely surprising, and the transitions between its phases are among the best-executed reveals in any browser game.

It matters here because it is the counter-argument to the idea that incremental games are empty. The mechanics change completely twice, the interface teaches you what it needs to when it needs to, and it ends, deliberately, in about four hours. It is free, it is text and buttons, and it is better than most games with budgets.