This is a very wide-ranging project and any help would be greatly appreciated.

More specifically, help is need in the following areas:
(1) The majority of the pages at the nodes along of the tree branches (the various subject areas) and at the end of each branch (the various topics within a subject area) are lacking an overview of the subject or topic.
It would great if a specialist or someone with good knowledge of the subject or topic could write an overview. An example of what is meant here may be seen at the demo version of the partitions of integers page.

(2) Secondly, almost all of the terminal nodes at the end of each branch are lacking a list of sub-topics within each topic. Once again, it would be great if a person with knowledge of the topic could provide a list of relevant sub-topics.
The person providing this list of sub-topics might or might not be the same person who would write the overview of the topic.
For an example of what is meant by a list of sub-topics, see the list of sub-topics within the mathematical topic of integer partitions at the bottom of the demo version of the partitions of integers page.

(3) Once the overview of a topic is written, and the list of sub-topics given, then it would be great if people with specialist knowledge of a topic could write the content for the sub-topic pages.
Of course, the same person could contribute to all of (1), (2) and (3) for a topic.

(4) I am unaware of classification systems for other areas of knowledge comparable to the 2010 Mathematics Subject Classification (MSC2010) system for mathematics.
Consequentially, the classification systems for these other areas of knowledge that are used on this web site lack the depth of the MSC2010 system used for mathematics, and it is likely that many of the current branches that end in general knowledge fields should further extended by breaking these general knowledge fields down further into more specialized topics.
For example, consider the branch Science -> Biology -> Biochemistry. Biochemistry is a vast field, and this branch of the classification scheme would need at least one more level of classification into subfields, possibly two more levels, before terminating at topics pages, each with their own list of subtopics.
As with (1), (2) and (3), it would be great if people with specialist knowledge of many of these fields, currently represented by the terminal pages at the end of branches in the classification scheme, could provide a further classification of these fields into subfields and topics.

(5) Finally, it would be much appreciated if you pass the web address for this site on to any person you think might be interested.