UFO: Alien Invasion
UFO: Alien Invasion is a free, open-source squad-based tactical strategy game built in the tradition of the classic X-COM titles. You take command of PHALANX, a multinational task force assembled to defend Earth from an alien invasion that has already begun. The game blends military realism with hard science fiction: you research captured alien technology, manufacture your own weapons and armour from it, and then send soldiers into turn-based firefights where every action point matters.
Key Features
- Two-layer campaign — manage the Geoscape (global strategy: base construction, funding nations, interceptions, research and manufacturing) and then drop into the Battlescape (turn-based tactical combat).
- Turn-based squad tactics — pin-point control of individual soldiers with action points, reaction fire, stances, and a strong sense of pace and danger.
- Research & reverse engineering — capture alien artefacts and technology, study them, then build your own upgraded arsenal.
- Base management — design and expand your bases, staff them with scientists and engineers, and equip soldiers and interceptors through the market and transfer screens.
- Destructible, multi-level maps — battles unfold in 3D environments such as farms, villages, bunkers and alien installations.
- Multiplayer — skirmish against other players, with a dedicated server (
ufoai-server) shipped alongside the game. - Moddable and extendable — the game logic is scriptable via Lua, and the UFORadiant map editor is included for building your own maps.
- Free and cross-platform — GPL-licensed, with no cost, telemetry or account required.
Why Use UFO: Alien Invasion?
If you miss the tension of the original X-COM games, UFO: Alien Invasion is one of the most complete free-software interpretations of that formula. It keeps the strategic depth — running a budget, choosing what to research, deciding which countries to keep happy — while making each tactical mission a genuinely tense, deliberate puzzle. Because everything is GPL-licensed and the data files are open, it is also an unusually good base for modding and for studying how a large turn-based tactics game is put together.
Use Cases
- Playing a full X-COM-style campaign without buying or installing proprietary software.
- Turn-based skirmish multiplayer sessions over a LAN or the internet.
- A free alternative for players who want deep single-player strategy rather than twitch combat.
- A study/mod base for developers interested in squad tactics AI, Lua-driven game logic and 3D level design.
Platforms
Windows · Linux (packaged in Debian, Ubuntu and Gentoo) · Android (port built from the upstream source tree). The latest stable release is version 2.5; a 2.6 development branch is in progress. The source data set is large — expect roughly a gigabyte for the full game with maps, textures and sounds.
Licence
Free and open source — GNU General Public License v2.0 (GPL-2.0). The engine source and game data are released under the GPL by the UFO: Alien Invasion project.
Similar open-source game
The Battle for Wesnoth — another long-running, free turn-based tactics game, if you prefer a fantasy hex-and-counter flavour.