Nightingale is a multiplayer game (although it can be played solo). It has recently shifted away from its former goal of having a "Shared World", MMO-like online environment, to offer more a of a small group cooperative experience. Nightingale plans to support up to 10 co-op players in a single game when it launches into Early Access sometime in 2022.
You can team up with friends or with players you meet during gameplay.
Once you invite friends to your realm, they can return to it at any time. If nobody is currently logged in to your realm, it will be frozen so you don't have to worry about upkeep.
The plan is to allow players from different parts of the world to play together (for example NA and EU).
Players can choose whether or not to join their friends in other realms, so you can be split between different realms. If someone else logs in, they will need to be given a party invite, and they will be able to choose as to who in your party they'd like to be teleported to.
Players can invite people to visit their respite realm and kick people from their realm. Currently if you invite someone into your realm they have total access to everything within it.
Players can have multiple characters, and any one of those can join any other player realms once invited.
Any items a player is carrying within their inventory will travel to whatever realms they go to with them, such as a friends realm or a randomly generated one
World save data is hosted in the cloud. The world save will be hosted by a specific player. Other players in your party will be able to continue playing if the host disconnects, but they won't be able to spin it up themselves.