The latest Humble Weekly sale features games from Kalypso Media, amongst them Tropico 3 and 4, marked as "Steam Special Edition" on the sales page
What's so special about the Steam Special Edition of these two games?
Taking a look at each of the game store pages on steam we see this.
The Steam Special Edition of Tropico 3 contains the following additional content:
Two additional maps for the sandbox mode:
Two additional costumes for the el presidente avatar editor:
Two additional accessories for the el presidente avatar editor:
...includes an exclusive island (Isla Nublar) and El Presidente avatar costume (Luchador) and 50 Steam achievements. El Presidente is back to rule it all!