I always wished there was a zombie mod purely focused on building barricades, closing entrances and trying to survive the round. Lasers are cool, but I always liked plank barricades.
Thanks to modern AI, and a little experience in modding from my childhood, I was able to build a project zomboid mod for Counter-Strike 1.6
You can basically search for items in dark corners, boxes, book shelves etc. (Admin places them for each map, saves them permanently). Pressing G opens the inventory. Inventory is actually interactable. Use/drop items work, items are saved to the server.
Map is pitch black, so you depend on finding flare items. Every round, there is a chance of electricity going off, removing all the flares. If you're lucky, you have a flare in your backpack.
Ammo is limited but generous (800 per weapon/round). Rounds are 5-6 mins. Unless you have a few other survivors, you're not gonna stop a horde without extra ammo items. Ammo items refuel your 800 ammo.
You can build barricades with knife which looks like a hammer. Pressing R switches between plank barricades and barbed wires. Plank barricades stop zombies fully, a single zombie can destroy it in 60 seconds. You're not stopping a group of them. You can stack plank barricades on top of each other up to 3. Barbed wires do not stop, but massively slow down zombies while they pass through. With knockback from continuous fire, they are very effective. Barbed wires are more common to find, while plank barricades require nails and plank.
At the end of each round (around last 90 seconds), a helicopter sometimes approaches to pick survivors. It waits for 15-20 seconds, and leaves. I found it is very hard to get to the chopper if there is a horde between you. A group of F15 jets pass over and bomb the whole map twice. Everyone dies except the survivors on helicopter.
Getting hit by zombies do not make you a zombie instantly. There is a 50% chance of getting bitten. Every attack makes you scratched, which bleeds you to death unless you use a bandage. If bitten, your screen gets darker, you slow down, and you turn in ~30 seconds. I always look for humans with less than 100 HP since they may turn inside the barricades :D
On some rounds, it rains, so you can't barricade outdoors. If you do, you get wet from rain, and eventually catch a cold, which kills you in a minute. You can keep towels you find around to dry yourself fast, or go indoors, but good luck if surrounded by zombies :)
Anyway, I'm really passionate about this, I've been testing it with bots and a few friends. I would appreciate cool ideas, too!