"Social bookmarking" started with deli.co.us and has largely been subsumed by reddit.
Beyond some level of complexity, Evernote, Obsidian, Notion, etc become bookmarking tools
...but the ultimate place to find the bookmark managers are in the Chrome and Firefox extension stores:
https://addons.mozilla.org/en-US/firefox/extensions/category...
https://chrome.google.com/webstore/search/bookmark?_category...
There doesn't seem to be any money at all in this space, and any really groundbreaking innovation will be folded in by the browser vendors, so I don't expect there to be much more thwn what's already here.