I think you are referring to Tiny MCE. I used it a long time ago but I think there are better alternatives. FCK Editor is used a lot but I think without their branding it can cost a few bucks. surrealcms.com ad a really easy and nice option, 25 bucks a month for unlimited sites. you put a editable class in whatever divs you wanted to and you could make an admin on your server with your branding for clients. would give them cms wherever the class was. They are changing up now to teir pricing and it can get expensive depending on how many domains you want to use it on. I think the unlimited plan is like 100 bucks a month now lol.
You can find a lot of tinymce type cms scripts with admin areas at envato's code canyon site for cheap. Be sure to look at the comments left to make sure there aren't any huge problems that may have been overlooked.
http://codecanyon.net/search?utf8=%E2%9C%93&term=cms
Best of luck