Seeking wisdom from the #Fediverse

Any good free or inexpensive #listserve #listserver solutions? I'm trying to help a 501c3 organization that's a group of cancer survivors exercising together on rowing machines and on the river in boats. Currently all communications are a Cc email list, but that's getting unworkable. Looking for a listserve or maybe old style BBS system. Preferably not Google hosted?

@quackitude managing social networking using email #listserver tech (I still do that) in the nineties, about half the list members were #lurkers, meaning those who read but didn't write. I interpret this as welcome interest by those who don't want to contribute to the content. A takeaway is we shouldn't post anywhere that doesn't have a vetted membership, something we don't want the world to know about us.