I released my CommonMark editor for Mac at http://www.textnutwriter.com, not free but has free trial. Many thanks CommonMark community provides a very clear specification to help me implement the render engine. It is written by Objective-C and passed all test case(v0.18).
TextNut has two editing mode: WYSIWYG and Markdown. Former is just a subset of CommonMark spec as 100% mapping rich formatting content back to markdown is impossible. Some on-the-fly trigger can be confused either. However, the markdown editing mode is 100% CommonMark implementation , especially, highlighter and HTML render as spec has very clear description and test cases for this.
When I do promotion, I found many people don’t know CommonMark yet. Just suggestion, if the community can provides a gallery page where lists all website/software that compatible with CommonMark? It could be a good place to let people know the CommonMark popularity?