Sharing this in case it's interesting to folks here. ANSIWAVE is a "modern" BBS that you can access in a terminal or web browser.

Home page: https://ansiwave.net/
Web version: https://bbs.ansiwave.net/bbs/

It has a built-in music programming language that you can embed in posts. Here are a few examples people made (hit the play button at the top):

Seinfeld
Druid II: Enlightenment
The Weight - The Band