@ellane Well, I would capitalize it. As others have noted, all of the authoritative sources (Wikipedia, Daring Fireball, the Markdown Guide, etc.) capitalize it. And I still consider Markdown to be a proper noun. While it is true that there are many variants of Markdown, they are all plainly called Markdown variants. And they all share, not just a common function, but a shared syntax. So it is not like Kleenex or Xerox, where other products with similar functions are often loosely described with the name of the most popular or the original product. If we were talking about "Markdown" being used loosely to describe all lightweight markup languages, then that would be a different case. But that is not what is happening here. Nobody uses "Markdown" to describe Textile, for example.

@ellane Yes, I miss Byword as well. It was a fave. Simple in all the right ways. And in the end, I'm guessing, probably too simple to earn enough money to sustain its maintenance.