Mostly @andypiper@macaw.social on the #fediverse - more links here.
I wrote a blog post about using Postmarks and contributing to the project https://andypiper.co.uk/2023/09/11/bookmarks-in-the-fediverse/
At the moment it is explicitly designed as a single-user implementation, although I’m sure it could be pivoted to become multiuser. I’ve simply set up my own on Glitch and it is working great! -> https://pipesmarks.glitch.me/
There’s also a really nice deep dive into the updates here.