Warning: this is a hello p.kde post, so now I can read minds; the page down key never looked so appealing!
OK, so I've been working on filemanagers for "a long time now". Back in the days when the Amiga was hot and hardware memory managers were a wonderful thing that would make a segv not take down the whole machine. Over the last roughly ten years I've been hacking on libferris. In that time it has expanded from a virtual filesystem to include index and search, virtualized extended attributes, RDF support, FUSE and rsync support and other party tricks.
Those with a keen eye will be asking why I am on this KDE planet when libferris "competes" with KIO, Strigi, Soprano etc. I have quoted compete because there is no clear winner and looser in projects that you do mainly for technical enjoyment. And there is no reason that libferris can not be used in a mixed fashion with other projects.
The last major release of libferris moved its RDF handling from redland to soprano, so at least the triples can be freely intermixed between projects now. On that note, I've recently created a new backend for soprano to use a memory mapped file with multi indexing as the triple store. See the ferris sf.net page for the boostmmapbackend tarball. The backend is in early days, but I'll take it for a walk on the n810 soon to see how well it works in that environment.
I am planning on adding spatial indexing and other tricks to the soprano backend which I've used for my maemo libferris metadata index module: