Listen up, deal hunters: between now and June 8, you can download Fortified on Steam for free. It's not a free-play weekend or anything--the game is yours to keep and play forever as long as you download it while it's free.
What is Fortified? It's a strategy-game-meets-shooter that's set in a stylized version of the 1950s. Martians are invading the Earth, and it's up to you to defend the helpless citizens from the extra-terrestrial threat. You do that both by setting up defense towers and by running around and shooting Martians directly with an array of weapons.
The whole thing has a purposely cheesy and cartoonish vibe to it, with aliens piloting flying saucers and robotic enemies straight out of pulp movies and TV shows from the '50s.