I'm not sure there's any one tool that fits my needs, and I've looked at a few, Zotero among them.

My understanding is that it's more a _bibliographic management_ tool.

There's also Calibre, which seems like it's a close solution, though that too is problematic, particularly at scale.

Another problem is that my laptop (as opposed to tablet) isn't particularly useful for reading formatted documents -- PDFs can't really be viewed _either_ one-up or two-up, and FBReader, which I like on mobile, formats ePub and similar eBook formats poorly (too wide, insufficient paragraph separation, unfamiliar controls), which is frustrating as well.

The tablet's much superior for _reading_ but even worse for _organising_ material.

Zotero (and Mendeley) addresses the problem of storing and organizing the content that you have access to, much like paid products such as refworks and Endnote. But, unless I am misunderstanding, it doesn't solve the problem of access to content. It's an excellent research tool though.