For those who easily suffer from information overflow, this (pruned) family tree may be sufficient to get a first impression of the current state of MD affairs.
Joplin currently aims to comply with CommonMarkdown, a broadly accepted standard in spite of John Gruber. On top of that, Joplin gives access to some extra features in the form of plug-ins.
I also mentioned two other lightweight markup languages in that post, AsciiDoc and reST. I don’t want to advocate those, because I have no experience with them. But it’s not a bad idea to have your eyes open in all directions.