Full text search
Quarchive crawls and indexes your all your bookmarks, allowing you to search - even when the term you're searching appears deep in the page. It also shows when a bookmark links to another one.
Private by default
All bookmarks are completely private by default but there are ways to share your view of a bookmark via a magic link if you want.
Quarchive shows Reddit and HN threads referring to your bookmarks, so you can more easily find people talking about things you are interested in.
Hooks into the browser
Just bookmark pages in your browser and the Quarchive extension will pick it all up. This is absolutely the quickest and easiest way to bookmark - no need to visit the site or use any special user interface.
Works in mobile browsers
Quarchive will pick up bookmarks you create in a mobile browser once they're synced to your desktop browser via normal browser sync. This gets around the fact that extensions cannot normally run in mobile browsers.
Free and Open Source
The source code for Quarchive (both the server and browser extension) is freely available on Github under the terms of the AGPLv3 or later.