I'm not sure what id Software, Bethesda, or Valve are thinking here but you can play all of RAGE for free until Sunday at 1PM (PT). If you already have Steam installed, all you need to do is click this link to begin downloading the game.

Yes, this apparently includes the single player component of the game. It's just odd that they would do this since most people are more than capable of downloading, playing, and beating the game in that time, thus removing the need to purchase it after this weekend. Huh, weird.