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Firefish Mastodon alternative
(joinfirefish.org)
This is a most excellent place for technology news and articles.
The creator of Mastodon said that he isn't going to add an option to set post length limits. I briefly tried to change it and wasn't able to make it work.
It's not configurable through the UI, but if you're the admin of an instance you can change the character limit with some fairly simple source code tweaks.