Secure Scuttlebutt Consortium on Github: https://github.com/ssbc ssb/ssbc is a fun and cool project built on solid code by smart people.
Blockchain tech was used to assure that messages created by others had not been altered in transit.
SSB ran into design limitations when the more recent developers tried to imitate something like Mastodon. It can work, but it's definitely idiosyncratic. It does tend to grow a large db, but space is rather cheap these days.