Annotation mode

[PT]

I'm looking for a mode for annotating files without modifying the
file's contents, so the anotations are stored separately from the
actual files.

The desired features:

- I want to add textual annotations to a file while reading it. I'm
thinking of hitting a key which pops up a window showing the existing
annotation (if any) for the file. I can edit the annotation and when I
close the window it is saved automatically.

- When a global annotation mode is enabled the currently stored
annotations are always shown for the current buffer.

- I'd like a browser which shows the existing anotations with the
corresponding file names, so that I don't have to open the actual files
if I want to see their annotations. The annotations should be
searchable. Preferably they could also be edited from the annotation
browser.


I tried to search with Google for a similar thing, but didn't find
anything. Thought I asked here first, before starting hacking my own
implementation.