Radioactive Sandbox

Radioactive Sandbox is a cross between the deathmatch and sandbox gamemodes with a post-apocalyptic theme. You aren’t forced to kill other people, but it is an option. If you aren’t too keen about killing people then you can explore the map searching for valuable loot, or go on missions provided by your faction’s trader. The whole point is that the gameplay is open ended and entirely up to the player.

You start off choosing a faction. There are 3 factions, each with their own strengths.

Bandoliers: A group of misfits that travel the wastelands looking for valuables. This faction has better selling prices at their trader, as well as increased payoffs for missions.
Exodus: A faction devoted to researching the environment and exploring dangerous areas looking for samples and stuff. This faction is the most scientifically advanced, and gives you access to various utilities including radiation filters, medication, flares and other things. These items are quite difficult to come across if you’re in any other faction.
N.M.A (Northern Military Alliance): This faction is a group of rebel militants seeking to dominate the wastelands. They have access to better weapons, and start off with slightly better guns.


Once you have chosen a faction, you are spawned in the faction base and left to do whatever you want. You can talk to your faction’s NPC and go on a mission for him so that you may earn money to upgrade your weapons and buy more supplies, or you can go off on your own and explore the map, finding loot and attacking other factions.



Other features:

Customizable item system. Create your own items unique to your server.
Day/night cycles that are map-independent. All you need is an env_sun in your map.
Item/spawnpoint placement gun for admins, so you can make the gamemode playable on any map.
Weapon base that supports scoped and non-scoped weapons.
Dynamic radar that detects various things.
Bleeding, radiation, and stamina system that directly affects the player.

Taken from http://www.garrysmod.com/news/?p=9281

Seems pretty interesting