Every time I see hype about Mastodon and the fediverse I miss the phpBB days. There was something special about the interlocking network of forums that didn't need to "federate" in any formal capacity. We just joined communities we liked and formed overlapping networks like normal people do and always have done. No one at the time felt any need to try to accommodate the whole world in one venue.
As someone who never understood the appeal of Twitter or Facebook, the new wave of FOSS social apps feels very alien to me.
There is a version of Lemmy (a fediverse clone of Reddit) with the phpBB interface: https://github.com/LemmyNet/lemmyBB