So this is one that I've been tossing around in my head to run as a pbp, and I still might.

It's based on the zombie survival game Dying Light. Which is basically what you get if you mix Mirror's Edge with Walking Dead. I personally love the heck out of this game, and play it all the time. It just hits a perfect little spot for me when it comes to video games. And given the way the system works for character advancement, I thought it would translate pretty well to the Talent tree system from FFG.

Basic Rules:

Pretty much standard Modern Day rules apply for equipment and stuff. Nothing fantasy or scifi level in the game, just animated corpses due to virus.

Obligation and the Duty mechanic would be included, though I'll probably call the Duty something else. The Duty mechanic would track the different efforts of the players to try and survive in the isolated city of Haraan during the outbreak. Each "level up" of the Duty system would allow them to introduce some new level of improvement to their situation, making survival that much easier as the story progresses.

Kind of Unique Rules:

The Freerunning talent and it's Improved version from the Star Wars books will be brought over, for obvious reasons, listed at Tier 3.

The city map will be broken up into regions, separated based on geographical differences or significant landmarks. (The elevated freeway being it's own zone, since it doesn't really meld easily into the sections below it. To try and make it feel like a dangerous, hostile place, each region will have a default set of penalty dice applied to it from the start. Really dangerous zones, will have automatic upgrades of difficulty dice, as well as setback dice, easier zones will just have setback dice. These penalty dice will represent the constant level of danger and threat that the shambling horde of undead. In the game, especially at the start, it's very dangerous to move around at all, as you have very few mobility related talents unlocked, and very weak weapons, and there are zombies everywhere. It's a constant state of threat and tension as you try and go out and accomplish the different quests. These penalty dice would reflect that, and they would apply to most, if not all checks made while out and about. Athletic/Coordination checks, survival checks (to scavenge for supplies), etc. Enough negative results will trigger things like another horde of zombie minions coming into your area, or the more dangerous viral zombies (fast moving, far more dangerous, Rival level difficulty) versions, being bitten, to make the situation that much more tense.

The dice penalties in the different regions can be permanently removed by concerted efforts on the part of the PCs, by taking initiative to solve problems. Or, if they aren't very creative on how to do so, various NPCs in the Tower (the safehouse for the majority of the survivors), will have missions they are willing to send the PCs out to deal with, to try and help their situation. They can also be removed for Duty rewards, but taking direct actions can have more immediate, and directed benefits based on player agency.

New Obligation: Infected. 20 Obligation, 25xp (if taken at char gen)

You've been bitten! You will slowly begin to turn into a zombie, unless you are able to regularly receive injections of Antizen, a viral suppressant. Each in game day, your Obligation for Infected will increase. The ONLY way to reduce it, will be to get a shot of Antizen. The problem is that Antizen is incredibly rare in the city, and trying to obtain it will be a serious challenge, involving dealing with dangerous foes. Taking this Obligation can potentially lead to your PC "dying" and turning on the rest of the party, think VERY carefully before taking it. If your Infected obligation is triggered on the session roll, you will feel the negative effects of the virus, causing spasms and seizures (loss of strain and/or setback dice to reflect this).

Inferior Weapons.

Pretty much every weapon (excluding firearms), will have the Inferior quality to them, as they are usually cobbled together scrap that people find lying around. Players who focus more on crafting related talents and character concepts will be able to improve the weapons with the necessary resources, but weapons will be unreliable at best for a while.

Loud Noise Bad!:

Firearms, while not subject to an Inferior ruling, do have a LOUD ruling. In that if you make a gun go bang, zombies will hear and come to investigate. So, while guns will be a very powerful and effective method of combat, you might make things worse for yourself by drawing more zombies to the location (specifically the fast zombies called Virals).

Beware the Night:

Nightfall, is bad. Like REALLY bad. The mutation properties of the Haraan virus can cause significant alterations to the infected, making for many varied types. The most lethal variety, the Volatiles (not Virals as mentioned above), are allergic to UV light, making them hide during the day, but come out to feed at night. They are incredibly deadly (Nemesis level difficulty), and can easily detect the living at night. Also, all zombies are noticeably more alert and active at night. Shambling zombies are less catatonic, and will more quickly react to your presence. Any activities taken at night outside of a safe zone will include increased difficulty, but the potential for significant rewards, see below.

The Night Brings Rewards:

Any sessions/activities taken at night, if you survive , will reward the participants with double XP compared to a normal session/mission.

Resources Matter:

Supplies are incredibly scarce. In the immediate aftermath of the outbreak, the city went into full riot mode. Looting was rampant, so finding supplies is hard. Having enough food to make it from day to day is a real struggle, forcing the survivors to go out and try and scavenge for supplies. The GRE (Global Relief Effort) periodically provides air drops of emergency supplies (food, medicine, and occasionally Antizen) but, as they are noticeable from anywhere in the city, other survivor groups will also attempt to obtain those supplies, and they might not be willing to share. Also there is no pattern to when and where the drops will land, so they might end up in dangerous locations for multiple reasons.

Crafting of new weapons and improvements to the Tower will require materials salvaged from the city, and players who focus on non-combat/physical talents will be incredibly important to actually utilize the materials the Runners secure on trips to the city. Players who don't want to go running around via the physical methods of the Freerunning talents, and fighting, will have just as important of a story, but it will be more narrative and drama driven, instead of running from zombies and leaping rooftops.

That's sort of the basic outline of what would make the setting "unique", based on the rules. Various tweaks and allowances for other talents not currently implemented would be considered on a case by case basis.

The setting is that an Olympic style global sports event was being hosted in the city, so people from literally every corner of the globe were at the location during the outbreak. So pretty much any character concept/background is viable, though I personally would limit to "normal" people concepts, and not things like "I'm an ex-ultra marine who specialized in urban combat and freerunning skills! And I was stealth based so I'm already really awesome at melee and throwing weapons!" The various NPCs that would give out quests can also act as Mentors in a limited capacity, allowing for quick improvement in areas the player wants to improve.