Glorpdown is plaintexty and mildly line-oriented, not totally unlike Gemtext. (Although at this point also a little less similar to Gemtext than it used to be.) I use it for this website.
This is kind of documentation, maybe mostly test page.
Headings
Lines that start with #, ## or ###.
one
two
three
Quotes
Lines that start with >.
blep
Horizontal line
Lines that start with at least three --characters.
Lists
Lines that start with *.
one
two
Preformatted text
Lines that starts with at least two `-characters. Following lines are preformatted text, until there's a line that starts with the same number of `-characters. Text-part of line that turns preformatted text off is caption. (Text-part of the one that turns it on can potentially be picked up by renderer for rendering things differently or something.)