"There's no such thing as "reputation" anymore. Who's there to spread the word?"
While the Commonwealth has been almost completely overrun with feral ghouls and disturbed survivors, the US Army has managed to keep hold of a few strongholds. Over the past 5 years, the military has learned not to trust the average wastelander, due to their tendency to be cannibalistic madmen. Be careful, the military has access to high quality weaponry and often shoot on sight.
The Federation is a group of well armed survivors occupying many sections of the metro. They are one of the few groups that do not shoot survivors on sight, and even welcome traveling survivors into their encampments. Currently, they are the most powerful faction of the metros despite recent defeats, and they are locked in a brutal conflict with the Metro Alliance. They have access to medium grade ranged weapons and gear.
The Alliance is a group of organized survivors occupying some sections of the metro and are locked in a fierce conflict with the Federation for territory. They are territorial, and while they do not shoot most survivors on sight, they do kill survivors that come too close for comfort or invade their territory. They too use medium grade ranged weapons and gear.
Themis Cultists are uncommon human enemies you'll find in the metros and in some regions on the surface. Following the will of a dark and mysterious god, the Themis Cultists are known to attack all survivors on sight. They tend to have a lack of firepower, and with the few firearms they do have, they're far from efficient or deadly. What they lack in firepower, they make up for in sheer numbers.
Maldenmen too lack when it comes to high-quality weaponry. Their arsenal is made up mostly of home-made firearms and hacking blades, such as cleavers and machetes. Driven mad by strange forces and satanic rituals, Maldenmen are extremely aggressive and should be avoided. Maldenmen usually aren't seen wandering the wastes and are most often encountered in the ruins of old settlements or in Maldenline. Be careful, these monsters wear durable armor and are highly capable melee combatant.
Survivors are people like you. Some are good, some are bad. Many Survivors will shoot on sight, just as you probably will. Some will stand their ground, only attacking if you invade their personal space. A rare few will actually be willing to trade with you. Survivors are, for the most part, a mixed bag. Some will have extremely high-quality weaponry while others will have crap. Some live in groups, some live alone.
The Hunters are extremely dangerous and resilient packs of survivors who are very proficient with ranged weapons. They usually travel with small packs of trained attack dogs which they use to brutally and efficiently kill other survivors. They have access to medium grade ranged weapons, and should be avoided if possible.