Windows 8 / Windows 7 / Windows Vista / Windows XP
Alliance of Valiant Arms is a free massively multiplayer online (MMO) game based on the Unreal engine. This first-person shooter game is based around a war between the European Union and the fictional New Russia Federation in a near-future Eastern Europe. AVA's beautiful graphics and variety of gameplay choices make it comparable to many for-pay FPS games like Call of Duty.
AVA offers you a choice of one of three classes, depending on the role you want to play: sniper (long-range damage), rifleman (balanced approach), and pointman (close-up damage, necessary to achieve objectives on some maps). Classes can eventually develop various special talents to make them more effective in their area of expertise. You can change your class if you get killed, which gives you some tactical flexibility.
The next step is to choose a weapon, or weapons, from the wide variety available. You can then choose from one of seven modes of play, from a simple deathmatch to tank escort or find-the-bomb missions. Then it's time to meet up with the rest of your team and hit the streets!
Like most free MMOs, AVA has a cash shop where you can pay to unlock special weapons and more customization.