This thread will be platform-independent and generally eclectic. It will not be a place for platform wars, nor holy wars in general. It will be a pleasant place for Dopers to come and share posts about software they have found interesting in good ways or bad.
Links are not required, but a description and a name would be very nice.
Bring your own sense of humor, and check your zealotry at the door.
Ahem.
fsv - 3D File System Visualizer: It is what it sounds like. 
fsv is a way to view the filesystem of a machine running an X11-based GUI in a very three-dimensional way. As the screenshots show, you can view your directories in two modes: A map view, which shows subdirectories and files springing, ziggurat-like, out of larger directories on the bottom, and a tree view, which creates a traditional view of directories based on nodes and leaves.
In both modes, you view the structure from the perspective of a flying viewpoint, which automatically zooms to the element you have selected (either by directly clicking in the graphic or by navigating the more traditional tree browser in the sidebar). This is a bit like being on an armature, because the movement (on my machine) is very smooth and very precise.
The relative sizes of the structures in the graphic are based on the relative sizes of the directories and files on disk: In map mode, the size is in square units of area. In tree view, size is expressed as height (leading to a somewhat vertiginous effect with especially large structures, as the floating viewpoint flies up to the top).
It’s a bizarre sensation, moving among your hierarchy like a ghost, making things expand and contract with the merest effort. The subroutines that implement the flying viewpoint’s motion give the illusion of a very fast, very controlled hover among large, solid objects. There apparently isn’t a physics model, per se: Acceleration and deceleration don’t exist, so while direction change is gradual, you go from a dead stop to full speed and stop on a dime. If you can’t stand first-person shooters because they make you motion-sick, this will do many of the same things. But if you’re a visual person, like me, you’ll probably enjoy getting a truly visual representation of your filesystem.
The visuals are dated, but that’s offset by the uniqueness of the whole program: We’ve dreamed of things like this since the earliest days of graphical computing (look at TRON), and private companies have made it a reality on expensive workstations, but only now is it accessable to the average home user with off-the-shelf hardware. If the graphics look like something out of an 80s music video, I’m willing to excuse it. It moves well and it looks very clean. After all, the NeXTSTEP is also an eighties user interface. 
A more serious gripe is that it’s just a filesystem viewer: There’s no way to manipulate things or even open a file from within fsv. This relegates it to the status of eye candy, basically. But hell, it’s fun.
Now, if you feel some sense of deja vu, you’ve either used fsn (the IRIX-only program produced by SGI with similar functionality) or seen Jurassic Park, at least the scene where the girl says “This is UNIX! I know this!” Yes, it was real software, not just random graphics painted on a screen. And, yes, it was fsn, because the JP people were using SGI systems.
Finally, I do know that XCruise exists. Never used it, but I know that fsv isn’t alone. I don’t know of any equivalent programs for GUIs other than X Windows.
