Minimalist Online Markdown Editor
this is a javascript webpage that can be saved to file and used offline to compose markdown in a browser tab. Not a service.
In preview mode your markdown is displayed in a wysiwyg pane.
you can also display your markdown composition as html source when the second pane is in HTML mode.
http://markdown.pioul.fr/
project at https://github.com/pioul/Minimalist-Onl ... own-Editor
clipboard2markdown
this second similar project also is a webpage that can be saved to file and utilized offline.
it lets you paste html or other rich text in to a browser text window and converts and renders it as Markdown.
http://euangoddard.github.io/clipboard2markdown/
project at https://github.com/euangoddard/clipboard2markdown
Using these two converters together allows one to convert a selection of html from a complex source into much simpler source.
once the selected html content from a large webpage is converted to markdown with clipboard2markdown, it can be pasted into Minimalist Online Markdown Editor in a different browser tab.