Yesterday I talked about using gist.github.com and Markdown. And I assumed that you wanted to work in "raw" markdown but that's like writing raw HTML - fine if you like it but not for everyone. A lot of people prefer a true Markdown editor where the tags appear visually as they might in Microsoft word. With a tool like this you can write in Markdown visually and then copy and paste (or export) into a Markdown file that you could put into gist.github.com.
Here are some decent Markdown tools:
- TextMate 2 (OSX); this is an OSX only coding editor which a markdown mode which works pretty well
- SublimeText; similar to TextMate 2 but works on Windows also
- Typora; top google hit; haven't looked at greatly
- MarkdownPad; free; looks like a dual pane NotePad i.e. markdown view on the left; writing window on the right.
- Marp Next - a tool for using Markdown for presentations; not for writing but just interesting that it even exists!
Personally I use TextMate 2 but I've been in that editor so long that I know it cold. As with any writing on a computer, use what works for you. There are lots and lots of tools for Markdown.