Keynote and Spatial Hypertext
Spatial hypertext people should take a close look at Apple's Keynote presentation software. even if they have to borrow a Mac to do so.
Keynote has a clever system of "guides" that help you align objects on each slide. In addition to of the familiar hand-specified guides (imposed top-down), Keynote sets up implicit guides based on the edges and centers of whatever objects are already on the slide.
It's simple. Few users, I expect, give it a second thought. But what we're doing is really interesting: the presence of an object implicitly partitions space, creating new geometries whenever we add or move something.