well, in fact instances of mastodon and pleroma too, but there are also web clients that allows to log in, like #brutaldon, that allows to have the fediverse on symbian. I'm able to log in with symbian on Friendica, but I'm not able to comment, seems to be an error in that part, so I was looking something to make it work. I saw an app called #gravity, but it doesn't seems to work anymore