Maybe two stop bits news

https://twostopbits.com/news

source: https://github.com/jgrahamc/twostopbits

Old skool: https://www.phpbb.com/

More modern: https://www.discourse.org/

If you want to be open open: https://github.com/mastodon/mastodon

https://github.com/lobsters/lobsters

http://arclanguage.org/

mastodon? That's probably the closest open source decentralized social media option to Twitter.

HN is a different beast.

Also, why is open source important for you?

The community is the real moat for HN, not the code.

https://github.com/sebst/pythonic-news

There's literally thousands of HN clones on github

I have a HN clone if you're interested