What things like Slack and WhatsApp use are not variants of Markdown, but entirely unrelated lightweight markup languages <https://en.m.wikipedia.org/wiki/Lightweight_markup_language>.
As for Teams, it looks like it’s much closer to Markdown (uses the same idiosyncratic/stupid link syntax), but still significantly incompatible even if they call it that. And my guess (as a non-user) is that it’s just an input method immediately converted to HTML or similar, not retained as text. So in that way it’s not Markdown either.
My least favorite Teams markdown idiosyncrasy is using (foobar) for emoji search instead of :foobar:
Technically speaking, Slack's markup language is mrkdwn.
That’s not technically, that’s marketingly (sure, it was presumably developers that named it, but it’s still marketing). mrkdwn is a horribly misleading name and they should feel guilty. https://hn.algolia.com/?query=chrismorgan+mrkdwn&type=commen...