Ok, something I have yet to see someone make in gmod is a random entity spawner.
In a nutshell, it would be a tool or a utility where you would tell it what you wanted it to spawn, be it an ent, a prop, a NPC, whatever; and you would tell it how often you want it to spawn the entity, and possibly the maximum limit of ents it can spawn. Then it would proceed to sprinkle the objects around the map, using some boundary sensing function to keep it within the confines of the map.
This way, we can actually have singleplayer games where it can surprise you, instead of you knowing where everything is already.
Some advanced options, if possible, could include things such as in what specific areas should it randomly place things.