To be honest, I find alternative media platforms a little disappointing. Like it feels as if a platform doesn't have a progressive code of conduct then it just becomes a hub for far-right politics, conspiracy theorists, and then some linux users who are like "it's not just for neonazis! I'm here too!" when the majority of the content is the other things.
This isn't necessarily a criticism of federated services, I mean Lemmy doesn't have that specific issue and I haven't used mastodon that much but as far as I'm aware it doesn't really have this problem either, so maybe there's something specifically about federation or the communities behind federated software that creates specific outcomes?
In general, I just wish the left would adopt more of these platform, it seems like most leftists have become very comfortable on mainstream platforms because most of our social views are in line with the tech companies behind these platforms (which isn't a bad thing of course), and we don't really have the influence/organization to threaten them where we disagree.
Also what's meant by echo chamber? I don't really like the term that much because it's often pretty vague and reduces human experiences to just their interaction on a specific platform. For instance, a place that's only for socialists isn't necessarily an echo chamber. For one, there's a lot of internal variety there and also when you live in a world that's predominately capitalist you're inevitably going to be exposed to and have to interact with capitalism supports and capitalist ideas.
This isn't a specific book recommendation, but a project/site. The project's called StandardEbooks and they clean up the projectgutenberg versions of books to make real good public domain books. At the moment they have some Kropotkin and the Manifesto