I’m looking for an online bookmarks manager whose organizational directories — whether they are called tags, folders, categories, labels, or whatever — can themselves be put into more than one directory. The only web services that I know even use such a system are Google Docs (where a folder can belong in more than one folder) and MediaWiki (where a category can belong in more than one category — the best known MediaWiki site is Wikipedia). I feel like I’ve seen every single bookmarking service out there, but I’ll bet there’s still more I haven’t heard of — so are there any that do this?
(By the way, I’m enough of a novice that I don’t want to do any coding or anything — I just want a pointer to a website that does this, whether for free or as a paid service. Thanks in advance!)