The hypertext model of NoteCards is based on the metaphor of 3" x 5" paper notecards. Nodes in the hypertext are called "notecards." Links (called "links") are embedded into the text of the notecards. "Browsers" are used to view and edit an overview of the notecard-link structure. "Fileboxes" are a hierarchial filing system to store notecards and other fileboxes.

The hypertext model of Neptune/HAM includes five objects. Nodes are called "nodes" and can be of three types: nodes for which versions are saved, nodes for which versions are not saved, and nodes for which all new content is appended to the old content. Links are called "links" and are bi-directional. "Contexts" hold nodes, links, and subsidiary contexts that are related to a particular topic (links can be made between nodes in separate contexts). "Graphs" contain all of the contexts in a particular web. "Attributes" can be recorded for nodes, links, and contexts, and can represent the properties of these objects or meta-data about them.

HAM is a general-purpose hypertext engine, whereas NoteCards is an application of hypertext to a particular task (idea processing). A NoteCards system can be built using HAM, but not vice-versa.

HAM contains two properties that NoteCards does not support: the ability to make two-way links and the ability to record meta-data for nodes and links.

I don't know. I suspect HAM because it is a more general application of hypertext.