UFO: Alien Invasion

I think this will be the last indie game for now with a shift back towards good games you might not have played or even heard of. I have a few in mind.

Anyway UFO: Alien Invasion is a nice free to play project that has been in development for some time now. They have translations for MANY languages and the game has multiplayer functionality.

General

It is the year 2084. You control a secret organisation charged with defending Earth from a brutal alien enemy. Build up your bases, prepare your team, and dive head-first into the fast and flowing turn-based combat.
UFO: Alien Invasion is a squad-based tactical strategy game in the tradition of the old X-COM PC games, but with a twist. Our game combines military realism with hard science-fiction and the weirdness of an alien invasion. The carefully constructed turn-based system gives you pin-point control of your squad while maintaining a sense of pace and danger.
Over the long term you will need to conduct research into the alien threat to figure out their mysterious goals and use their powerful weapons for your own ends. You will produce unique items and use them in combat against your enemies. If you like, you can even use them against your friends with our multiplayer functionality.
UFO: Alien Invasion. Endless hours of gameplay — absolutely free.
The game takes a lot of inspiration from the X-COM series by Mythos and Microprose. However, it's neither a sequel nor a remake of any X-COM or other commercial title. What we as a team wanted to make is a brand new experience that tries to surpass the quality of games from 1992, rather than simply recreate them with flashier graphics.
We also believe that open-source projects don't need to be disorganised or badly-managed. We work together in a friendly and professional way, with a clear vision for a game that we know is worth playing.

Combat mission.

Geoscape.

Geoscape with Nation overlay.

Gameplay

Like the original X-COM games, UFO:AI has two main modes of play: Geoscape mode and Tactical mode.
In Geoscape mode, the game is about base management and strategy. You manage the activities and finances of PHALANX, controlling bases, installations, aircraft and squads of armed-response troops. You'll research new technologies and use their results in battle against the aliens. You'll launch your interceptor aircraft to shoot down UFOs and dispatch dropships in response to alien activity across the globe. You can build, buy and produce anything you like, as long as your technology level and your budget will allow it.
Geoscape mode employs easy-to-use time buttons to control the passage of time however you like, automatically pausing whenever there's an important message for you to see. Research will progress and items will be produced as time passes.
In Tactical mode, the game is about taking command of your team in various missions to combat the aliens wherever they might appear. Instead of pushing imperonal armies around on giant maps, you use only the team of soldiers you've assigned to deal with this mission — the same soldiers which you've managed and equipped to your satisfaction in Geoscape mode. You may find civilians and other bystanders during the mission, being targeted and executed by the aliens, or just getting in the way while you're trying to protect them. It's a dangerous world, and some of your men will die.
Tactical mode uses a turn-based system, where your team and the aliens take turns to make moves. During your turn you can order your troops to move around, fire their weapons, throw grenades or use other equipment, etc. Each soldier gets a certain number of Time Units (TUs), representing the total time they have to act during the current turn. All actions in Tactical mode require Time Units to perform. Once a soldier is out of Time Units, he or she can't do anything more until the next turn.
Your mission objectives will vary for each mission, and there are many to perform as the aliens' terrifying plot unfolds. You'll have to watch your back, be quick on your feet, and take the fight to them.
If you don't, humanity is doomed.

Base screen.

Game engine

The game engine is based on a heavily modified version of id Software's Quake 2 engine. This doesn't mean that UFO: Alien Invasion is a modification or even a total conversion of Quake 2. It is a stand-alone game and doesn't require Quake 2 or any other program to run. All you need to play UFO:AI is a computer running Microsoft Windows or a supported version of Linux, and the installer from our website.
Our updated engine has modern OpenGL graphics and special effects, increased texture resolution, hardware-accelerated clipping of map layers for toggling between levels, a new animation system for player models, powerful artificial intelligence, and many other exciting features. Is was developed as a joint effort with the Quake2World project.

Soldier equipment screen.

Multiplayer

You can play UFO: Alien Invasion with your friends via LAN or Internet connection. One player controls a human team while another player takes command of the aliens for a bloody head-to-head battle. UFO:AI also supports cooperative team play with multiple players on both sides, up to a maximum of 3 teams for each side, 6 players total.


I've only played it a bit but it shows promise. There aren't really any good gameplay videos as far as I can tell but you can find a few meh ones on youtube.