Reanimation Zombie Survival Card Game

Reanimation is very highly rated at Board Game Geek. And it is free.

Warbucks is currently up on a Kickstarter, but the print-and-play version is free. The author describes it as a deckbuilding game like Dominion, but with territory control:

The deckbuilding component is more action-focused than engine-focused, but I’m not ashamed to say that I borrowed a fair bit from Dominion, and learned a lot about card interaction, pricing, and design from reading dominionstrategy.com and playing lots of Dominion when Isotropic was still running Dominion games.

The base of the game is a territory control game, but without the dice rolling that you have in Risk. If 4 armies attack 3, 1 survives. That’s a fun half of a game (surprisingly), but what makes it interesting and provides a random element are the cards. Basic troops can move and attack, and that’s it. More interesting behaviors like jumping over enemy lines, moving farther, and hitting harder as well as responses that you can play on defense are in the cards.

There’s also a strong diplomacy/negotiation component to the game — it helps to convince people that you’re not a threat so they go after the other players, and there is bribery built right into the game to provide one more method of inducing cooperation from your (temporary) allies.
Your army holds territory, territory produces money (WarBucks), and you spend money on more troops and tech for your troops in the form of cards.

Zeppelin Derby Print and Play Card Game

Zeppelin Derby is a free print and play game that uses just 17 cards. From the game description:

It’s race day! Aircrews to your Zeppelins! In this fast-playing racing game for two intrepid Zeppelin pilots, the players race their airships by rolling dice and playing cards — including a few dirty tricks! Who has the moxie to cross the finish line first?

Witch Hunt Print and Play Card Game

Witch Hunt is a print-and-play card game with just 18 cards. It’s a “traitor” style game with a twist.

The Engine Empire Card Game

The Engine Empire is a print-and-play card game that requires only 18 cards. From the description:

In a dystopian alternate reality, four great powers vie for control of the continent. Each Empire’s soldiers lay siege to opposing cities, while their war efforts are funded by exotic exports and ingenious inventions. Only one state will orchestrate their limited resources into an Empire Engine powerful enough to lead them to victory.

It has gotten good reviews on Board Game Geek.