Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
NotePlan - Make plans inside an individual markdown note for every day in your calendar. Use it as a journal for your daily tasks and plan todos in advance. For Mac, iPhone and iPad.
Joplin - Joplin is a free, open source note taking and to-do application, which can handle a large number of notes organised into notebooks. The notes are searchable, tagged and modified either from the applications directly or from your own text editor.
markdown to web - Convert markdown to online web page
Google Keep - Capture notes, share them with others, and access them from your computer, phone or tablet. Free with a Google account.
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.