Speaker notes are supported in reveal.js, PowerPoint (pptx), and beamer output. You can add notes to your Markdown document thus:
::: notes
This is my note.
- It can contain Markdown
- like this list
:::To show the notes window in reveal.js, press s while
viewing the presentation. Speaker notes in PowerPoint will be available,
as usual, in handouts and presenter view.
Notes are not yet supported for other slide formats, but the notes will not appear on the slides themselves.