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After more than 15 years on the platform formerly known as Twitter, Cambridge is leaving X
(www.bostonglobe.com)
This is a most excellent place for technology news and articles.
There are several non-profit had their own instance, like ACM. I recall Mozilla used to do, but I am not sure if they still does.
How expensive is it to have your own instance?
I don't think it is terribly expensive, a lot of (somewhat large) domain specific academic instances are maintained by grad students with donation from academics. As far as I know, many of them are in good financial standing.
It can be as low as €4/month + domain name, see:
https://docs.joinmastodon.org/user/run-your-own/#so-you-want-to-run-your-own-mastodon-server