I guess there are not many philosophy-related hypertexts out there: one of them, trying to change the way we usually engage with the philosophical work, is for sure HyperNietzsche. Its most interesting feature seems to be the "principle of contextualization":

This principle is one of the most original aspects of HyperNietzsche. While the user navigates the site, moving from one page to the other, this feature makes available precisely those documents that are relevant to the page that is presently being viewed.

For example, if the user selects a manuscript page, the system immediately makes accessible, without the need for additional complicated searches, all the transcriptions and translations available for the page, as well as all the relevant text-genetic paths and all the critical essays that refer to the page.

If the user selects a critical essay, the contextualization mask will present a list of all the Nietzsche texts and manuscripts cited by the author of the essay, and a list of all the contributions that are cited in, or that cite, the essay being viewed.

I didn't manage to put my hands on a tech paper about it yet, so I can't really understand what's the backbone of the system's navigation feature. However, at a first sight I remained a little disappointed with the application. Slow, a lot of broken links, and moreover the works which can be browsed are limited (The Wanderer and His Shadow only_?)._
Should we be waiting for a second version?

Anyways... the interesting features, I think, are :

- big amount of scanned images (basically all the Nietzsche's work we can browse)

- while you flick through the pages, a contextual set of related resources appears on the left

- users can publish their contributions, in the context of the resource they are reading (contributions are peer reviewed)

- multiple contextual view on a work (panorama, browse, rhizome)