Knowen is collection compact knowledge nodes assembled into directed acyclic knowledge graph. Public root is the top-most node of the public hierarchy (it has no parents). Any other public or publicly visible node is its direct or indirect descendant.
The idea is to keep every node compact, limited to about page or two of text (plus relevant figures, attachments, notes). This way it is easy to digest and convenient to modify. Each node is a logical unit, self-contained for its level of generality/specialization. The hierarchy goes from the most general -- the Public root (this node) -- to more specialized, all the way to the research frontier. There is a simple guiding principle for building the hierarchy: In order to be able to understand the content of any node, it should be sufficient to have understood its "ancestors" (parents and so on), but not siblings or children. And vice versa, the higher level node should be a generalized (compressed) version of its children.
Physics, Mathematics, Chemistry, Biology, Linguistics, Philosophy are examples of the level of generality that may be appropriate for direct descendants of Public root. For the second generation, the descendants, e.g., of Physics are Condensed Matter Physics, High-Energy Physics, etc. The number of descendants of any given node should be kept small, less than 10 or so. If more children appear, it is likely that the common features of some of them can be effectively combined into a more generic node, with the details transferred into grand-children. For instance, an intermediate node Natural Sciences can be created under Public root that combines general aspects of Physics, Chemistry, and Mathematics, with themselves becoming children of Natural Sciences. Rewiring is easy!
Note that all nodes that all public nodes that descend from Public root are public -- they can be read and edited by any logged in user. If you are interested in creating your private project with access limited to you and your collaborators, create a child node under Private Root -- this will become a top-most node of your private project. Later on, you can make your private project visible to the general audience by adding an appropriate public parent (Public root or one of its descendants) to the projects top-most node, or make it completely public (by detaching it from Private root).
Feel free to edit any node as well as add descendant nodes to any node, including this one (if you have a better way to explain the idea).