Timehunters is little more than a WIP concept so far.
The basic idea is that, for whatever reason, certain people have access to time travel. This will include the party. The exact nature of the time travel is undecided, it could be high tech sci-fi, steampunk time machine or fantasy magic. It could also be a vehicle style machine or a handheld device.
Either way, the time travel is limited. Each time they travel, they need to repair/refuel/recharge their time machine, and so they are trapped in each time period until they can do so. This means they have to get involved in the periods they travel to in order to survive. Once they complete the appropriate quest in each period, they move on to the next one until eventually they achieve their goal. Each period will take a few sessions and be a mostly separate arc.
The purpose of using time travel is also undecided. Perhaps the party are time bandits hoping to steal treasure from other times, or they are a form of police, hunting said time bandits. They could also possess a faulty time machine and keep ending up in random time periods while just trying to get home. Perhaps they have a very specific person to meet or object to find and must keep traveling till they find it.
TBD
What system to use?
Most likely Cogent Roleplay
What world is this set in?
The real world, alvergia, its own world
Where are the party from?
The past, the future, outside of time
How does time travel work?
Portals, vehicle-like machine, handheld device, spells
The party are a squad of temporal police who must make sure that historical events occur as they should. Time-travelling meddlers keep trying to change events for their own ends, the party must counter this. Events can vary slightly, the time stream will fix that, but major conditions must be met. These conditions are the things that time-travelling meddelers may attempt to change
For example, if the party goes to England in 1066, they may have several conditions to meet:
A time-travelling assassin may attempt to kill William before, or during, the Battle of Hastings. Alternatively, someone may attempt to poison the English troops before the Battle of Stamford.
An important detail to remember is that the goal is to make sure history moves as it's supposed to, not to do the right thing. Sometimes this may mean helping the "villains" in order to keep history on track.