Jira. Its WYSIWYG editor is goddamn awful. Runner-up goes to its sibling product, Confluence, for the same reason.

It is amazing how bad Confluence is, and it still seems like the best choice for an internal wiki. I have been close to building one myself, but for now I have withhold.

Anything that includes WYSIWYG with no opt-out is shit. Slack also tried to pull off this crap but thankfully backtracked after the complaints.

Slack needs a tweak to the message editing. Inline editing would be nice, instead of having it the new message area.

JIRA can do markdown.

its their own strsnge version of markdown though, which just adds to the flame of hatred imo

if you were ever so unfortunate to have perfectly marked up content and previewed in the visual mode, only to save it and loose a ton of formatting (seems in visual mode the actual data source isnt the same as markup) upon save...