Hello
I've searched across the forums, gh repo, and SERPs looking for answer, if this forum board can be used as a comment system on a flat file CMS. Is this possible in quite simple manner? Maybe there are some widgets or plugins making this possible I'm not aware of?

Unfortunately, flatboard cannot be used as a comment system since this is an entire forum script and cannot be modified down to just a comment system.

It's not about tinkering down the whole bbs to transform it into comment system.
The whole logic is there, especially for content administration purposes.
I'm not aware how fboard index page work and if it's a custom made frontend, but it shows latest posts.
What I"m asking for is the ability to somehow show a forum thread on a webpage with the ability to add a reply using some kind of a widget.
Alternatively load thread's content on a webpage, and if somebody wants to "post a comment" (read as: reply to thread) he would be redirected to this thread on forums.
There's nothing useful in documentation, nor I did find any websites using flatboard that would mess with displaying some of the forums threads on their websites, blogs, etcetera.

btw. the reply form doesn't show up. Tried in 3 different browsers. I had to mess with dev tools to be able to reply.

Oh I get it now, yes you could make a plugin using Plugin hooks - Documentation, so far there hasn't been anything for that. I'm currently busy to be able to make any extensions right now.

btw. the reply form doesn't show up. Tried in 3 different browsers. I had to mess with dev tools to be able to reply.

Fred would have to fix that.

  Get inspired by the blog.php page.

I'm working on a brand new version of Flatboard with all the code revised. Flatboard 5 will have a demo very soon 😍
 

  You mean Flatboard 4?. Since you are on flatboard v3.5 it would be 4 not 5.

Formatting versions:
Major.minor[.patch]

Besides that, I can't wait to see it 😊