The best replacement for tinymce is ckeditor.

The best alternatives to tinymce are rated as following:
★★★★★  ckeditor
★★★  fckeditor
★★★  jce
★★★  codemirror
★★★  redactor
★★  nicedit
★★  markdown
★★  wysihtml5
★  aloha
★  wymeditor
★  aloha editor
★  xinha
★  jce editor
  fckeditor drupal
  elrte
  cke

Your alternative for tinymce is not listed? Suggest!
Speaking about tinymce, one probably shouldn't forget about elfinder.

Other search terms related to tinymce and their ratings are:
★★★★★ elfinder
★★ spell checker
You have in mind a companion for tinymce and it is not yet here? Propose!



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