Fortified is a unique blend of third-person shooter, real-time strategy, and tower defense genres. Developed by Clapfoot, this Windows game takes place in the 1950s during a Martian invasion of the United States. The game features a wide variety of sci-fi archetypes, including a jetpack-wearing heroine, a space cowboy with a shotgun, a secret government agent, and a battle-hardened Marine captain.

The gameplay allows players to fight off the mechanized invaders in various ways, either by personally shooting them or by building a network of defensive structures. The strategic aspect of the game is not as elaborate as in a pure strategy game, but the tower defense elements are robust and offer a great variety of units and tools. The game's visual style is inspired by the comics of the 50s, neon lights of the 80s and 90s, and the cold dynamics of the 00s. The locations in the game feature quotes and allusions to famous works of science fiction from the fifties.