Discord is used in the FlightGear community as an alternative to Mumble, TeamSpeak, FGCom or Ventrilo.
Discord is a free voice and chat software that can be downloaded as an app or used in a browser.
| Note Its advised that you create a permanent account, instead of creating guest accounts as some people create duplicate accounts which clogs up the member logs and makes it more difficult to @mention people.
Furthermore many other FlightGear servers exist that you may need an personal invite to join. The easiest way to find them is to go to the FlightGear server and ask or ask in forums.