OS filesystems like Mac OS X have filesystem tagging (terrible) but what happens when we move that file to Windows or Linux. We lose the tag data.
Applications like Notes Apps (Evernote etc), Todo list/PM tools (Jira/Ashana/Ora) all have their own bespoke tagging implementations -sometime using tag groups or multi-level tagging, sometime combining with categories but rarely is their ian yinteroperatleabaility between these aps whern it comes to tag meta data. Websites with CMS systems like wordpress have tags too. Wouldn't it be great if you could author your post in a markdown add relevant tags and publish to the site with wp adding the meta-data from the markdown file. The list goes ...image tags, analytics tags, keyword tags, social media messaging hashtags. If we had one universal system perhaps based on a standard like XMP for meta-data tags... I don't think it can use the name file name of note title etc - we need something like the sidecar file.. like a spotlight index file that goes with the data entity wherever it goes across app, across OS, across devices, across from filesystem to website etc etc. Furthermore what if everyone could have their own tag backpacks - these are group of popular tags associated with user (would work especially well with some thing like gravitar) so when tagging your social media message, post, rich media content update, comment etc you can pick not only from the sites platform popular tags but your own bag of face tags that you carry about wherever you are in apps, websites, machine, Os etc