Used it for ages, it worked better than TinyMCE back in the early days (though I think they're probably equal now.)

Interestingly, I swear FCK was the creator's initials - I wonder if the app's name change is a reflection of a name change on his behalf? ;)

There is a “notes on the new name” section on the linked article:

“For years we have been fighting with a relatively important issue with FCKeditor. While its quality has been strongly accepted, its name brought us troubles, mainly inside English speaking countries. The fact is that the initials of Frederico Caldeira Knabben have an unfortunate match with the most used English bad word.”

It's fairly popular as a "drop-in" wysiwyg editor in custom-made CMSes, afaik.

Yes, we do at www.bharatmoms.com and of all the rich text editors(js based) we tried, this worked out to be the best.

Wow, you run an online community for mothers in India? Very interesting stuff. Didn't expect such a thing to exist. How's the site coming along?

Yeah, we use it on a fair few client sites. Works pretty well but sometimes struggles a bit with pasted Word content (but most things do).

It used to be called FCKEditor, which is used on a lot of big sites such as pbworks.com (which was also formerly known as pbwiki)

Well, it's been available for quite some time as a MediaWiki (also dokuwiki etc.) plugin, so I don't doubt those numbers.

I used it in a website for a customer.