Some addons make these NPCs available through spawnmenu. The entity names are listed in parenthesis. How do you spawn NPCs in Garry's mod? These NPCs can be spawned through the console, with the command 'npc_create *entityname*'. Spawn settings can be changed via the 'Spawn Editor' in the Q menu options.
Not only zombies can be spawned, but any class that works normally in the game. As of now no other addons/gamemodes do this without manually placing NPC spawners everywhere. FAQ about Gmod Random Npc Spawner Convert Is there an addon that will spawn random NPCs? This addon will constantly spawn random NPCs within a certain distance of any player.