Exactly, text editors are such everyday staples and yet it's easy to take for granted that they are open source. Vim is often the first package I install on new systems when not already present and, outside of my web browser, is certainly the program I use most.

On that note, I'll add Markor to my favourites list. It's absolutely the best Android markdown editor/viewer I've found to date, and it works beautifully with Syncthing folders.