Textpattern Resources mentions three WYSIWYG content editors which I built around August 2014. The trio is kuo_tinymce_cdn, kuo_jhtmlarea_cdn and kuo_cleditor. They can be downloaded from Textpattern Resources or from my Textpattern Plugins section. My Textpattern site has a download counter for files. According to it TinyMCE plugin has been so far downloaded 200 times, jHTMLArea 109 times and CLEditor 83 times.
The most popular WYSIWYG editors, which I've made, for Textpattern