Deathmatch Classic or DMC is a multiplayer mod of the popular first-person shooter, Half-Life. It was released as a free download concurrently with the 18.104.22.168 patch of the game on June 11, 2000.
DMC was conceived by Valve as a tribute to id Software, and is essentially a remake of the multiplayer component of id's Quake. It took three months to develop.
The original release included five maps converted from Quake. The gameplay is similar to Quake deathmatch, with essentially the same weapons (except the one for melee combat, which is Half-Life's trademark crowbar instead of the original axe), armour and power-ups. DMC also imitates Quake's physics, which allows an advanced player to gain a lot of extra speed or jump very high by using a number of movement skills such as bunny hopping and rocket jumping.
The default game speed in DMC is somewhat slower than in Quake. The weapons scale from the basic shotgun to the rocket launcher and the "shaft", a powerful directed energy weapon. Three kinds of bonuses are scattered over the maps, which give the player a temporary special power: "quad damage", "invulnerability", and the "ring of shadows" which turns the player into a ghostly, almost invisible figure.
Source: Wikipedia, "Deathmatch Classic", available under the CC-BY-SA License.
This game is also available as a stand alone game on Steam.