Wolfenstein: Enemy Territory

Enemy Territory is a free multiplayer FPS set during WWII. It was originally planned to be released as a commercial expansion pack to the popular FPS Return to Castle Wolfenstein and later as a standalone game. However, due to problems with the single-player aspect, the multiplayer portion was released on May 29, 2003 as a freeware standalone game. In early 2004 the source code for the game logic (not the game engine) was released to the benefit of its modding community. The game uses a modified RTCW engine, itself being a modified Quake III: Team Arena engine (which has been open-source since 2005).
Wolfenstein: Enemy Territory is an online multi-player game, where the players interact with each other over a network in two teams (Allies and Axis) to defend or destroy mission objectives. The game is playable over the Internet or a Local Area Network. Like many online games, cheating and exploit communities exist. To counter this, the game has support for PunkBuster, an anti-cheat solution.
There are six officially released maps (North Africa Campaign: Gold Rush, Siwa Oasis, and Seawall Battery; Europe Campaign: Rail Gun, Wurzburg Radar, and Fuel Dump), as well as hundreds of custom maps made by the internet community. On each map, the offense needs to complete a certain set of objectives within a limited amount of time. The defense needs to keep the offense from completing objectives until time runs out. Some objectives may be optional, and some objectives can be carried out by either team. These minor objectives assist the team completing them. Depending on Game Mode the action will continue on another map (Campaign Mode) or the same map (Objective Mode, Stopwatch Mode, Last Man Standing).
In all but the LMS mode, dead players respawn all at the same time, every X seconds. In the default maps - assuming that the server settings aren't changing it - Allies spawn every 20 seconds and the Axis every 30 seconds, the only exception being Rail Gun where both have a 20 second spawn. With default settings, you can see the spawn timer in the right side of the screen. Experienced players should watch the timer all the time - dying to a 1 second spawn practically means losing your position (and a life, if the server has the rarely used Limited Lives feature enabled) and resetting your health and ammo, while a 30 second spawn can be deadly if there are only a few players. A good tactic is to find out the spawn time of your enemy, for example looking at the mission timer, and time your attacks so that every dead opponent will have to wait a full time spawn.
In the official six-map campaign (most common on public servers), Allies are offense for all but one map. In Stopwatch Mode (most common for locked or LAN servers) two teams - most common setups: 6vs6 or 3vs3 - will play the same map twice, once in each side and the winner is determined of who have the fastest offense (it can be a tie when both teams defense manage to keep the offence from completing the objectives until time runs out).
Players may earn experience points in several skill categories. All character classes may earn points in Battle Sense and Light Weapons. Class skills are generally restricted to the current class, the exception being Heavy Weapons (the Soldier class skill).
Players have certain abilities based on their character class. The player has a Power Bar that provides 'power' for their special abilities. The power bar regenerates slowly. Constructing the Command post speeds up the recharge rate though. Players have up to eight weapon slots, depending on character class. The classes that are available are engineer, soldier, field ops, medic, and covert ops.
Players can gain experience in three skills: Battle Sense, Light Weapons, and a skill determined by their current class. Certain class skill benefits remain with the player even if they change classes. Benefits from general skills are available regardless of class. Once a player has accrued enough experience points in a particular skill, the skill is automatically advanced to the next level, providing the player with a new ability or advantage. There are four attainable levels in each skill, awarded at 20, 50, 90 and 140 experience points.