Markdown is a text to simple HTML conversion tool for web publishers. It allows content writers to write using an easy-to-read and easy-to-write plain text format, then convert it to valid XHTML format.

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Sublime Text

sublime-text
Available for different platforms (Windows, Mac, Linux) is the best editor you can find if you are a programmer or developer. Although not specifically designed for content writing purpose but is an excellent choice that I recommend to anyone looking for a powerful and flexible editor. However, you can install some plugins for easy Markdown editing:
Markdown Preview : Allows quick export to HTML written texts.
Markdown Editing : Applies more appropriate theme for Markdown files in this format.
MarkdownLive: Creates a small local server to preview a live document, but requires NodeJS and the installation is a bit more complex.

Qute

Qute
Qute is an ideal choice for users who want to focus on writing content and avoid creating text option details. Ability to directly edit the Markdown. Selection of different visual themes and fonts. Allows exporting to HTML or LaTeX and PDF (via Pandoc ). If you like to minimize distractions editors but want something more powerful than Qute is best for you. Available for Windows, Mac and Linux

MarkdownPad

MarkdownPad
One of my favorite editors is MarkdownPad, available for Windows platforms only. Besides having a comfortable and intuitive interface, offers many interesting features such as: Editing content in portrait or landscape, support tabs to edit multiple files, processes Markdown, ability to apply different CSS profiles, support for different language, allows exporting in HTML or PDF format. It has pro and free version.

Texts

text
Although it may seem a simpler alternative to the HarooPad, it nevertheless is a less interesting application. Texts is useful to edit the content in a visual way, without using the Markdown format explicitly, but does work similar to MS Office. Visual editor that requires no explicit format. Support issues and possibility of manual customization of CSS. Allows exporting to HTML, DOCX, RTF, EPUB, PDF and LaTeX. The application allows use of free version for over a period of 30 days, after which a license must purchased. You can download Retext, if you are looking for a similar application for GNU/Linux.

MDCharm

MDCharm
An alternative of MarkdownPad is MDCharm. It lacks some features such as format customization, but old version for GNU/Linux has all those features. This application aimed at users looking for an editor halfway between easy to use and customizable. Side Menu with project tree view. Processes and MultiMarkdown. Support tabs for editing multiple documents. Lets you customize keyboard shortcuts. Customize the CSS styles in the document. Allows exporting to HTML, PDF and ODT format. The software is free for WIndows and Linux platform.

DownMarker

DownMarker
Available for Windows. If you are looking for a simple and minimalistic application that allows you to simply write in Markdown, your choice should be definitely DownMarker .

MarkPad

MarkPad
MarkPad is only available for WIndows and supports Windows 8. MarkPad Markdown allows you to create documents in Windows 8 Style. Integration to create documents for Jekyll. Support tabs for editing multiple documents. Multilanguage support available. Processes Markdown and Markdown Extra. Create blogs and publish articles directly to GitHub.

HarooPad

HarooPad
Probably one of the most powerful Markdown editors is HarooPad. Available for Windows, Linux and Mac platforms. One of its main features is that it has a simple and friendly interface for users with little knowledge. Includes a quick chop as a dropdown on the left menu. Processes Markdown, Markdown GitHub Flavor and allows customization. Full support for customizing themes and CSS styles. Allows exporting to HTML format. It’s free, cross-platform and you have the source code available on GitHub .