Half-Life Deathmatch: Source
Following on from the release of Half-Life: Source, Valve announced the development of Half-Life Deathmatch: Source on 10th June, 2005 (http://www.steampowered.com/Steam/Marketing/June10.2005/). The game was eventually released on 1st May, 2006 and was available with all purchases of Half-Life: Source (https://store.steampowered.com/app/360/HalfLife_Deathmatch_Source/).
Half-Life Deathmatch: Source is a port of the deathmatch component of the original Half-Life to the Source engine, though like Half-Life: Source, there a number of small differences, like the addition of 3D skyboxes and the absence of the Magnum .357's zoom and the gasworks
map. The lack of zoom for the Magnum .357 may have been an oversight, and the absence of gasworks
can probably be explained by it being in the initial release of Half-Life. According to Michael Labbé of Threewave Software, Threewave Software was responsible for the port.
In 2013 Half-Life Deathmatch: Source was updated to the Source 2013 branch of the Source engine.