A long, long time ago ... there was a browser extension or maybe an iframe, that allowed you to "comment" on public websites. Of course you weren't really commenting on the actual website, just some form of overlay. Anyway, it quickly devolved into lawsuits and rude comments if I recall correctly.
check out https://margin.at !
There have been several efforts. At one point the W3C were working on a standard protocol for it: https://www.w3.org/annotation/
Do you remember any details about the name of the software, or the cause of the lawsuits?
I had a similar idea, funny to hear it's been done and ended so badly.
I don't recall any lawsuits, but whytheluckystiff made one 20 years ago. https://ruby-talk.ruby-lang.narkive.com/buiXXTZh/what-is-hoo...
Don't know if it matches with the lawsuits, but could've been Third Voice (1999-2001).
I believe it was https://web.hypothes.is/