Utility Concepts ...

All organizer facets need security and access control.

Organizer facets = notes, tasks, to do, checklist, calendar ...

All need hierarchy.

All need grouping. Folders.  Etc.  Labels. Tags.

Heck - just think of them all as objects in a filesystem.  Perhaps we want to type the drectoriew, the folders, as MS has done with WinFS - so that a list of tasks = a folder, a directory, that contains nothing but tasks.  So you can't put something else in there by accident.   But note that you want to be able to add notes, etc., everywhere - i.e. you want to be able to attach notes and calendar items to the folder/directry that cntains a list of tasks, etc.

All need the same edit tools: drag and drop objects to folders/labels, and vice versa.  Multiple selection. Etc.

All need the same capabilties.  It's just a question of providing convenient defaults. Convenient views.  E.g. its most convenient to display calendar items in a grid. But you probably don't want that to be the default way of seeing To-Dos or Notes./  (Althoygh it would be nice to be able to do so.)

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The biggest differences between filesystems/folders/directores and objects like text notes/calendar items/to-dos are granularity, orderedness, and embeddedness.

Files tend to be relatively coarse grain.  (Although the Reiser FS can efficiently support 0 an 1 charcater files.)

Files in a directory/folder do not necessarily have an order.  (Although there may be one.)

Once you transition from a list of files in a directory to a text file of notes, you have really transitioned.  You are no longer in a file browser anymore.  You're in a ext file reader or editor, or an HTML browser.  You can transition back, but you have gone through a pahse change.

... For a long time I have been thinking about representing filesystems as XML.   Obviously, XML can represent any filesystem.   Moreover, XML can also represent the internal structure of the files.   XML has the orderedness and embeddedness that a filesystem lacks.

We can imagine an XML browser that can transition from browsing filesystems to browsing objects.   Or a family of browsers, some specialized for the filesystem subset of XML, some for the text file, calendar file, etc.  But all having the same basic capabilities.

The filesystem may just serve XML up to the browser.  Making it essentially transparent whether what is being served is a directory listing, or file contents.

...This is like JSON versus XML.  Filesystems are like JSON: hierarchical, but not really ordered.  File contents often have more structure than JSON. Orderedness and embeddedness are two standard sch aspects of additional structure beyond JSON.