Not sure if this will fit the bill exactly, but have been looking for something like this to accompany knowledge base note tools like Roam, Obsidian, etc., since those don't work that well with web content IMO. Using Zotero at the moment, which is fine for something not web-based. are.na is maybe another similar service aimed at content beyond bookmarks. klobie looks good though!
A couple of suggestions: I like the 'card view' of the board pages, but assuming one has a lot of tags, and many bookmarks per tag (or even many bookmarks for a single tag), I feel the 'overview' you get with the board page kind of vanishes and the individual tags take over. Something like a fixed height option for the cards that becomes scrollable would be nice. Alternatively, each tag becomes a separate page, with the bookmarks being listed once you enter the tag page instead of the board page, but not sure if you want that kind of hierarchical structure. Oh, and maybe a tighter column view might be nice!