Mark Text, a popular Markdown editor, had a new release over the weekend (0.16.0, followed by 0.16.1 to fix a bug). This update brings an experimental spell checker, file encoding support, support for custom fonts, and much more.
Mark Text is a free and open source Electron Markdown editor for Windows, macOS and Linux. It features CommonMark and GitHub Flavored Markdown, seamless live preview, multiple edit modes (Typewriter, Source Code and Focus), and support for code fence for all popular languages.
Prefer to use a GTK3 Markdown editor instead of an Electron one? Check out Marker. There's a Gedit Markdown plugin too.
Other Mark Text features include inline and block Math support, TOC (table of contents) syntax support, keyboard shortcuts, search and replace, paragraph / word / character count, 6 built-in themes (both light and dark), and the ability to export to PDF, HTML / styled HTML.