A currently unfinished mod for half-life 2 that includes co-op and deathmatch maps, however cheats need to be enabled to get the real feeling of gameplay.
list of debug keys
(require "sv_cheats" to be set to 1)
pressing "i" gives all weapons and equipment
pressing "o" spawns an antlion
pressing "v" activates/deactivates no clipping mode, which allows you to freely fly around the map without brushes or entities getting in your way
credit to some users on gamebanana for some content
http...