A blog at your own address
Each account gets a public blog on its own subdomain. Published posts are readable without logging in, and each one carries a canonical URL pointing at your address rather than a shared host, so search engines credit the author.
RSS that works in both directions
Your subdomain publishes an RSS feed of your posts. On the bare domain, the same feed path becomes the planet feed — everything everyone publishes, newest first.
That means you can syndicate outward to any reader, aggregator, or newsletter tool, and you can equally read the whole instance from one subscription.
A public index, not a walled garden
The planet index lists recent public posts with real links to each one, and it is rendered in the initial HTML so crawlers and plain readers see the posts rather than a loading spinner.
Visibility is per post. You choose what is public and what stays private; publishing is never a side effect of writing.