Factions in Fonline 3 are communities. They are divided in two groups, NPC-driven and player-driven. Your character can only be in one faction at a time, either a player one or a NPC one.
The player-driven factions list is on the Player-Driven Factions article.
NPC factions are official, like the Vault City faction or the Enclave faction. Joining one of them is useful, because you will be able to meet instructors for professions, and to make some private quests. But you won't be able to be in a player-driven faction until you resign from your current one. You can join and leave a faction freely, but (unlike player-driven factions) it will affect your reputation, so be careful.
See the NPC-Driven Factions category for more details.
|NPC Factions||Player Factions||Bases||Town Control||Reputation|