A Unreal Tournament mod.

Tactical Ops is a freeware Unreal Tournament multi-player modification, which transforms the game into a team-oriented Action-Based-Semi-Realistic anti-terrorism simulation. Similiar to Counterstrike for Half-life, TacOps features real guns, such as the Glock 21, the Desert Eagle (for big brave balls), the 9mm MP5 Navy, the AK 47 and the Steyr Aug.

The entire game is based around two teams; the Special Forces (Police and SWAT), the protectors of the world against terrorism, and the Terrorists, who strike fear in the hearts of innocent and unwary civilians.

Unlike standard deathmatch gameplay, TacOps requires slow advances and caution. When you die in the game, you stay dead until the whole round is over. This can take several minutes, and therefore novice players who get killed early usually get bored, because the have to watch and wait a lot.
But when you get a feel for the game, and learn that you have to be a bit more careful than in other first-person shooters, this game can be a great rewarding experience.

The realistic weapons and detailed maps (featuring different "standard terrorism" scenarios such as a skyscraper, a dam, a ship, a subway station, a train station, etc.) give plenty of opportunities for both the SWAT team and the terrorists to play hide and seek.

Although many people are already playing the current release, Tactical Ops is still in development. New weapons, new maps, and AI players (bots, probably the most requested feature) are still ahead.