Steamworks.SteamParties
This API can be used to selectively advertise your multiplayer game session in a Steam chat room group. Tell Steam the number of player spots that are available for your party, and a join-game string, and it will show a beacon in the selected group and allow that many users to “follow” the beacon to your party. Adjust the number of open slots if other players join through alternate matchmaking methods.
Events
The list of active beacons may have changed
The list of possible Party beacon locations has changed