Storyspace was created by theorist
Jay David Bolter (author of the germinal text
Writing Space), hyperfiction author
Michael Joyce, and chief engineer
John B. Smith. It is a hypertext authoring environment, created well before
Tim Berners-Lee conceived of the
World Wide Web, and first released for public purchase in 1990. Michael Joyce's
Afternoon, cited by
Robert Coover as "the granddaddy of hypertext fictions," was created in Storyspace.
Storyspace works a bit like an outliner (that is, in fact, one of its view options). There is a hierarchy, with the name of the document at the top level, and the initial spaces right underneath it. Spaces, the basic unit of a Storyspace work, are somewhat analogous to a node in E2: they have a title, and an underlying writeup. (Unlike E2, there's just the one writeup, and of course no voting or listed author or any of that.) In the main Storyspace view, spaces look and work a bit like bastardized windows. Spaces can contain other spaces within them, which you see as little mini-space-icons inside the space (when looking at it in the default view). Double-clicking a space's "title bar" (which is much more compact and abstract than a regular window's title bar) opens its text, and double-clicking its body opens a view of the spaces inside it.
The thing that perhaps best distinguishes Storyspace documents from hypertext in other media is their visual nature. Spaces remember where you put them. You can arrange them into a happy face if you want. This, more than their hierarchical nature, is what gives Storyspace documents their sense of space, and justifies the choice of Storyspace as a medium over more accessible forms. (Storyspace does, incidentally, export HTML.) Many hyperfictions published by Eastgate let you switch to the Storyspace map view and look at the structure of their text screens, even navigating the hierarchy instead of following links.
Links are visual too in Storyspace. If two spaces on the same level (contained within the same space) link to one another, you see the link right there, as a nice curvy arrow. Links to spaces elsewhere show up as a little abbreviated arrow, just long enough to show the link's name. (Links are named in Storyspace, so you can refer to them in guard fields, on which more in a moment.) From the text view, in read mode, links are followed with a single click. You can create a link from a specific range of text, or you can link a whole space (in which case a click anywhere in the text will follow the space link).
The behavior (that is, the destination) of links can be given some simple logic, with what Michael Joyce calls guard fields. Guard fields are simple codes with which one can say things like "If the reader has seen space 'foo,' send them to space 'bar,' and if not, send them to space 'Helen Shapiro.'" With guard fields, links can be given some texture. Multiple links can also overlap, or be placed on the same space but given different guard fields. The resulting behavior can be very complex, creating what Joyce calls "hypertext contours." Visiting the same space and clicking the same word twice in one reading may produce different results (and, in Joyce's fictions, usually does).
Reading works created in Storyspace is usually somewhat disorienting - deliberately so. Critics like Sven Birkerts decry the excessive control granted to the reader in hypertext literature, but I have a feeling their negative reaction is driven primarily by the basic infantile revulsion you get when forms of control that you're accustomed to having (like being able to see how many pages are left before the end, or the power to skip ahead) are ripped away. However, Storyspace does give the author the option to let readers view the underlying structure freely. There's no reason you can't create something in Storyspace that ends up being perfectly rational and graspable (David Kolb's Socrates in the Labyrinth is a wonderful example of how linearity and hierarchy can interweave with chaos to the benefit of all involved).
Unfortunately, Storyspace is at version 2.0 for Macintosh and Windows, and that was a while ago. The Windows version, at least, is starting to look very long in the tooth, and frankly, Storyspace's user interface has always been too obtuse and weird. Storyspace 3.0 really ought to be rewritten, and (while I don't desire to take food off the tables of the good people at Eastgate Systems) that probably means open source, given Eastgate's resources. An open-source clone of Storyspace's basic concepts and file format, with an improved interface, would be of great benefit to hypertext scholars and, ultimately, to the market for Eastgate's publications.