This is the Mathslate editor adapted as a standard plugin for TinyMCE4. In order to install Mathslate into a local installation of TinyMCE4, copy plugins/mathslate to tinymce/js/tinymce/plugins/mathslate. You may need to change the url at the top of plugin/mathslate/mathslate.html to a different value to use https. Otherwise you may run TinyMCE4 from CDN by copying this directory to a web server, or by visiting https://dthies.github.io/tinymce4-mathslate.
Mathslate is copyright 2014 by Daniel Thies firstname.lastname@example.org and licensed under GPL version 3. Mathslate was originally developed for use in the Moodle platform. These files are a crude adaptation from the Moodle TinyMCE plugin.