CKEditor has an open source version that can be used in Drupal (check version). These are the license details:
CKEditor is distributed under the GPL, LGPL and MPL Open Source licenses. This triple copyleft licensing model is flexible and allows you to choose the license that is best suited for your needs. http://ckeditor.com/about/license
However, please notice that by default, CKeditor comes with a button to add media files to the content. That button offers a popup window that could allow the user to find and to upload files directly to the media repository, but for it to work it needs and Add-on for the CKEditor called CK Finder, and CKFinder is not Open Source (http://ckeditor.com/support/faq/ckfinder#question2) and it requires a paid license.
Now, the Drupal core comes with a Media button that can be integrated into the CKEditor and allows to insert media in the content and upload it directly to the server, however, then it means that the user will need to insert the media with one button and manage image attributes with another, it could be tricky for users but with proper training it will be fine.
Felipe is a one of the first (and old) spartans at inQbation, senior developer focused on the back-end, but with front-end capabilities, PHP fan and certified engineer with more than 15 years of experience