"A Hypertext Help System" builds upon A little hypertext system and adds more markdown features along with a TOC. dgw::hyperhelp is an extension which adds documentation, standalone application mode and usage examples,
shtmlview - hypertext widget with support for HTML 2.0 and Markdown display, including images and basic table support.
See the iwidgets hyperhelp widget: hyperhelp
Some people have balloon help (tooltips) in mind as the canonical help model.
TkWebView has a procedure that defines a simple help viewer.
WISH User Help is the world's simplest hypertext help system (as far as the author knows, anyway).
bll 2018-8-23: BallroomDJ includes a help program that reads the help text from a file that has sort-of-wiki-type styling for headings, italics, bold, bold italics, images, line breaks, tabs (fixed position), tags and internal links to other topics in the help file.
I use the tabs and line breaks to create simple table displays. Or just line breaks to create a simple list.
The tags are not only used for the internal links, but also used to automatically build a table of contents and when the program is run, a tag can be supplied to position the help for context-sensitive help. The tags have an associated level and the level is reflected in the table of contents treeview.
Now, this help program is currently loosely tied into BallroomDJ, but it's not too difficult to detach (it used to be a stand-alone program). I can help with that process if you are interested, as I know what pieces need to be removed/replaced.
A sample of the help text file can be seen at: https://sourceforge.net/p/ballroomdj/code/ci/default/tree/bdjdata/bdjhelp.txt