TeXstudio - TeXstudio is an integrated environment for writing LaTeX documents.
Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
Overleaf - The online platform for scientific writing. Overleaf is free: start writing now with one click. No sign-up required. Great on your iPad.
Minimalist Markdown Editor - This is the simplest and slickest Markdown editor.
LyX - LyX is a document processor.
Typora - A minimal Markdown reading & writing app.