Four Against Mars is a solitaire pen-and-paper sci-fi adventure game with RPG elements. It belongs in the Four Against Darkness family of games and uses a similar gameplay system. You can currently order the pdf from Drivethrurpg.com and Ganesha Games' website, but if you don't wish to print it yourself, a bound book version will come out sometime in the near future.
In Four Against Mars, you play as a group of civilians in a 1950s small American town. You will first create your characters, choosing among a scientist, a medic, a survivalist, a combat specialist etc, and give them different abilities, weaknesses and weapons. As the game progresses, you will get to level them up and raise their dice rolling strength: they begin with a D6 and can go up to rolling a D12.
The town is under an alien invasion. As soon as you encounter a Martian, a Venusian or a Reptilian enemy, you will be doing a stealth check, then try to defend yourself. You can also attack the aliens, and resolve the fights by rolling your weapon die. The book includes a town diagram that shows where events take place: farms, cottages, church, restaurant, hospital etc. You will be rolling dice and consulting charts to see which location you are moving into, and what you find there. Not much information is available yet, but for fans of the Four Against series, 4AM will feel both familiar and new.