Ghost is a free open source blogging platform. You can host it yourself free of charge, but the developers also offer a paid service for those who don't want to self-host.
With Ghost getting ActivityPub support, it means people on Mastodon etc will be able to follow Ghost-powered blogs.
@FediTips So for the layman, is Ghosts (open-source) kind of like Substack (closed course) in a way?