It took me a while to remember (find) something I used years ago that was pretty neat in that you could not only limit which pages were editable, but also limit what part(s) of the page were editable (like webedit pro). It didn't have a WYSIWYG editor, but used textareas (this was a long time ago, before all these WYSIWYG editors were developed).
I was thinking that it should be pretty easy to integrate FCKeditor, SPAW, or one of the other editors I mentioned into it, as they are designed to be "plugin editors" for textarea fields. If you did this, it would seem you would have a very serviceable, and freely customizable FOSS replacement for webedit pro.
At any rate, I finally tracked it down. EditTag is a small collection of GPL licensed perl scripts that:
There are a few other features, password protection, and even a "customized" version where another user has added a version of htmlarea to it to provide WYSIWYG editing. That version used an "older" version on htmlarea which only worked with IE5.5 or above, but I think it would be a good "working model" for adding a modern WYSIWYG editor in the same manner .
I also came across an very neat derivative of EditTag by a Dreamhoster! Eric Kittell has developed a PHP package that works in a similar manner to the perl program. I can't provide a url directly to the script as Eric's site is "flashified", but you can find the script easily enough from his home page. From the "readme":
Eric has licensed this under the GPL, so it is freely modifiable also (it is also recent, as it carries a 2006 copyright notice). Again, it should be almost trivial to add one or more of the WYSIWYG editors to function with the textarea fields.
I think adding a modern WYSIWYG editor to either (or both) or these is very doable given the quality of documentation available for integrating the editors into existing programs. I might even be willing to help if you have difficulty with it, as I think this is a very useful class of product that needs to have a WYSIWYG version that is GPL'd