If there was a cross-platform, open database that could be used by commercial or open-source apps, then we could have a competitive market on "organizing UX" without worrying that a policy change at our favorite indie developer or global conglomerate would orphan the data. E.g. WebDAV, CalDAV, OPML, a dublin core metadata file which accompanies artifact files (photo, pdf, warc), sqlite db, camlistore, git-annex, ..? Currently using a combination of these tools for cloud-neutral kb:
Mind mapping: iThoughts HD on iOS, export to PDF
Idea capture: OmniFocus on iOS, export to XML
Contextual & tag search with preview snippets: xapian + recoll on Linux
Web clipping: Print To PDF (wkhtmltopdf) on Firefox or Epub
File tagging: Calibre on Windows, plus SumatraPDF for viewing epub, pdf, djvu
OCR: Abbyy on Windows
Nepomuk was/is kind of a solution like that, though mostly targeted at the desktop. It would store all the data in an RDF database (with layers to speak other protocols, like IMAP) using standard formats, and applications would interact with it instead of having their own storage layer.
Supposedly RDF caused poor performance and it was replaced by https://community.kde.org/Baloo which uses sqlite+xapian. The nepomuk ontologies live on in the Digital.ME research project, which seems to be a research prototype in Java for a "cross-device social semantic desktop", but there's no active dev community.
Maybe the semantic desktop should be a semantic server? Run it on a dedicated PC that also serves as NAS. It would be a relatively small price to pay for a secure pkb with cross-platform clients.
