https://www.humblebundle.com/summersale2014-free
All you have to do is put in your email and you're done. Hell, if you have multiple emails, you can get more copies since it's one copy per email. After that, all you need to do is go to your email, click on the link which Humble Bundle will ask you to, and then log in to Steam via your browser when prompted to. And that's it.
If any of you want to confirm that this is not a prank, Google it on the internet. Not to mention that the link does have the official Humble Bundle address in it. I know it's a bit hard to swallow, but hey, EA gave away Battlefield 3 for free with the only cost being having Origin installed.
Keep in mind that this is only for a day, so don't wait out too long.
If you don't know what Tropico is, it's a town management simulator with a lot more politics, flexibility, and bizarreness involved (I think, never really played a Tropico game before). If I remember, I think Tropico 3 was the epitome of the series, that or Tropico 4 even though a lot of people were upset with it because of all the DLC.
Have fun being president.
