StackOverflow actually uses MarkDown, a popular html syntax. When writing answers and questions, it provides a WYSIWYG editor for common MD functions such as bolding, underlining, headers, links, etc. Comments are usually short and at the most contain some code
or a link.
If you really need to you can google for a WYSIWYG online editor such as StackEdit that you can write your posts in.
Heck Yes Markdown seems to offer a useful api.