PRISM: Guard Shield is a free fps developed by U.S Army.

It seems that a new version is available for download.

Link to Official Site

The Army National Guard and Rival Interactive are creating a first person 3D shooter called PRISM: Guard Shield that contains a unique blend of stealth operations and fast action game play. The game focuses on the unconventional application of new and emerging weapons and surveillance technologies in the war against terrorism. PRISM takes place in the near future with the player becoming the newest member of a highly secretive homeland defense unit known as PRISM. PRISM: Guard Shield focuses on familiar locations in the US such as Washington, D.C. and San Francisco, CA. When terrorist activities are suspected or potential targets are identified, players are called into action.

PRISM: Guard Shield is being developed simultaneously with a game for the commercial market called PRISM: Threat Level Red. Players will be immersed in a unique gaming experience that draws players into a world that blurs the lines between commercial entertainment and America’s secret struggle against terrorism using tomorrow’s technology and weapons.

Gameplay Features
. 3 environments
. 3 multiplayer game modes (Co-operative, Death Match, and Team Death Match)
. 8 near-future weapons
. 7 characters with 3 unique enemy types
. Up to 32 players online
. Recognizable landmarks
. Use stealth tactics to gain the advantage over the enemy
. Unique Hover Camera at the player’s command
. ‘Night Vision’ capability to see in the dark and surprise the enemy
. Silenced weapons and Taser stun-gun allow the player to take on the enemy
silently
. Highly configurable Co-op multiplayer modes
. Real ray-traced reflections
. Picture-In-Picture capability during game play