The group I currently play with uses a group chat over SMS/MMS. But I’m going to be DMing a campaign with an open table, so I need something more persistent and flexible. I’ve used Discord in the past but IMHO it has way too many features.
What have you used to keep in touch with your players?
My group does discord, we play on VTTs so built in voice chat was a requirement. You really don’t need to engage with any features you don’t want/need to. If you’re the only DM you can be the server owner and leave everyone else a default user.
For a more FOSS answer I think Matrix would cover basically everything that discord does. I haven’t used it that extensively but it seems to be the best discord alternative when dealing with larger groups where you may want several text channels.