I came upon this while looking up things related to Zettelkasten or "card box" style note taking. It would be helpful to have more information about the tool on the page rather than all of the testimonials (which don't really answer why this is better than something like WorkFlowy except that one references it). Without signing up all you can infer from the schematic and comments are that this is like a wiki that reports back-links.

As a separate comment, I've had really great success using Zotero for this purpose. I already ingest all the journal articles, book references, etc I read into it using the Zotero browser plugin. You can tag items and (bi-directionally) link related items, and add notes with its inbuilt HTML note system. I just have one folder that contains my notes and link them to each other. You can also attach reading notes to the bibliographic entries themselves and have separate folders for project specific notes. A weakness however is that the links do not appear as hypertext in the body of the note but instead in a pop-up menu.