Here is a general one for people playing Freeciv with a multiplayer setup. Pretty much anything goes on this server and it's also a great place to get relevant Freeciv info about all multiplayer related things.
https://discord.gg/dANdHrV
Here is the discord invite for longturn.net discord server and it's also a great way to get info about new longturn games, setups and developments.
https://discord.gg/9CU9PFz