At the current state it’s only single-user, but I’m working on a multi-user implementation. It should be available as soon as I have a proper implementation for the ActivityPub Group actor (similar to what WriteFreely already does, where you have a Group @blog actor that aggregates post from multiple Person actors). That would also unlock full compatibility with Lemmy/NodeBB and other threadiverse implementations. But it takes a while to get done right - and a multi-user set up is also a design challenge when your selling point is to have a blog running on a single folder with Markdown files.

About a free instance, it’s not currently available (you’ll need your own domain and host and then you can just spin up a Docker container), but AFAIK YunoHost is considering adding it to their offering.