Wolfenstein: Enemy Territory is a downloadable, free-to-play multiplayer game in which players wage war as Axis or Allies in team-based combat.
It's a team game; you will win or fall along with your comrades. The only way to complete the objectives that lead to victory is by cooperation, with each player covering their teammates and using their class special abilities in concert with the others.

Players join the fray as one of five distinct character classes each with unique combat abilities.  The Covert Ops can steal the uniforms of fallen enemies and perform covert reconnaissance behind enemy lines, while Engineers can plant and diffuse land mines as well as construct battlefield structures including bridges, guard towers and forward operations bases in the midst of combat to gain advantages for their team. Medics provide health and revive fallen teammates, as Field Ops use their binoculars to mark enemy positions for a Soldier's mortar barrage.

To play this game you will need to run the Enemy Territory Ultimate Installer.  The latest version of this is 1.6.

You can find the ultimate installer at http://etui.kashu.fr/

If you are adventurous, you can also try out an alternate version of the game client called Enemy Territory: Legacy
The download page for Enemy Territory: Legacy can be found here.

Click here to check out some other Wolfenstein: Enemy Territory servers.