I've been looking this morning for a WYSIWYG editor to integrate with one of the personal projects I'm planning to make. It's going to be a WIKI that would allow anyone in my team to add, edit, view or search entries for best known knowledge. I'm planning on proposing the app to them a day or two before I leave the company. I also wanted to test the PHP MVC framework(Just an ambitious thought) that I am working on (somehow patterned after the Servlet and JSP technology, though not 100%). Anyway, I wanted a WYSIWYG editor similar to what we have here in devpinoy. It's good that I found TinyMCE . Though I haven't tried it yet, I am quite satisfied with the demo that I've seen in their website. Here's a little info about TinyMCE from their website:
What is TinyMCE?
TinyMCE is a platform independent web based Javascript HTML WYSIWYG editor control released as Open Source under LGPL by Moxiecode Systems AB.
It has the ability to convert HTML TEXTAREA fields or other HTML
elements to editor instances. TinyMCE is very easy to integrate into
other Content Management Systems.
This might not be something new to a typical web developer. But nonetheless, this should be very exciting to integrate with my app! 
If you have any other suggestions that are also free/opensource then I'd be glad to take a look at it.