This is a port of Deathmatch Classic to FreeHL/Nuclide.
It's basically just QuakeWorld deathmatch, but with a splash of Half-Life. This means that sprays and all that stuff work. Even crouching works in this particular version for the time being.
Since it's still a Half-Life mod technically, you need FreeHL set-up to play this addon.
If you have the unreleased Threewave content installed, it'll turn on a couple more entities and features. Do not ask about this, it's still a WiP and replacement content is being made by a a community member as of this writing.
There's a small compat layer so you can play on existing HL:DM & Quake III Arena maps without .ent file hacks or having the port levels manually.