CKEditor is completely free and open source under the Open Source definition.
Not only is the program free but there is also a wide range of completely free plugins and skins that are available for use with CKEditor.
Dont buy this product as the company does not honor the terms and conditions of the purchase. After the Froala company was acquired all original commitments has vanished and old purchases and their respectively conditions are no longer honered. I have tried to get the companies attention but they do not intend to change this. A bad situation for any customer. A shame since the original founders (and owners) build a great product with a great culture. That has definitely changed for the worse.
A side-by-side comparison with open-source (free) alternative (see below) makes you wonder why you would use this (and why it has so many recommendations......).
If you require it to be even more flexible don’t forget that you can use our clear API and callbacks in almost any situation.
Checkout the API docs here.
You can also expand the functionality with the existing plugins listed here and even create your own.
The image drag and drop works fantastically (see the short demo in the Youtube clip in the summary) and also supports upload to Amazon s3 out of the box.
Redactor supports a floating edit bar that appears when the user selects the text they want to format. It's really nice if you have trained users and want a cleaner interface. You can also easily modify what icons you want to show. See a demo here.