CGameRulesProxy

is a base class for all "gamerules" entities. It lets the developers set arbitrary rules for maps and the whole game, and for handling many events. The games that use this class (the multiplayer games specifically) all make their own game-specific derivative of it. Most games allow players to place the gamerules entity in Hammer, but even if the mapper doesn't place it, the entity will still get created once the map loads due to it being quite important.