Technically all of them work already, just with subpar UI. If you follow a Lemmy community on Mastodon by searching for it like a user, the community’s posts show in your Mastodon timeline.

Each community post appears as a Mastodon post boosted by the community “user”. Threaded replies all work.

To make a post to a community, you tag the user in any top-level Mastodon post.

There’s a survival game called Grounded that’s basically this but even smaller. And a coop story action/adventure called It Takes Two that does the same.

Obsidian is a fantastic note taking app that focuses on cross-linked notes, so is effectively a personal wiki.

It has a paid add on that lets you publish it to a website, or you can just do it yourself since the files are all Markdown.

I’d look at karlicoss’s personal data infrastructure for inspiration (or perhaps deterrent).

Take a look at intelligent tiering for a good no-frills solution! Each item automatically determines its tier based on how often you access it.