Topic notes
general notes (not including endnotes or footnotes)
Ruby annotations in ConTeXt
To-do notes in a document
Multiple series of endnotes for critical editions
Add notes on document development
Notes in the margin, even where \marginpar fails
Make numbered notes in the margin
Notes in tables or images
Miscellaneous tools by Mark Wooding
Macros for marginal notes, in Plain TeX
Minipages with marginal notes
Integrating notes into the bibliography
Notes at end of document
Notes after every paragraph (or elsewhere)
Tables with captions and notes all the same width
Notes in longtables
Make a to-do list for a document
Marking things to do in a LaTeX document